Knittable, thermally insulating, and sustainable aerogel fibers enabled by ion-mediated hierarchical assembly

Domain: chemistry
Published: 2026-03-02
Editorial outcome: minor_revision

Abstract
Aerogel fibers (AFs), while promising for personal thermal management, are constrained by an inherent trade-off between mechanical robustness and thermal insulating performance. To resolve this mechanical-thermal coupling issue, we propose an ion-mediated attenuated Coulombic assembly of recyclable heterocyclic aramid nanofibers (HANFs) to construct hierarchical AFs, enabling programmable manipulation of pore size and porosity. HANF-AF features a dual-scale porous architecture, comprising a nano-porous core and a macro-porous cellular shell, which encloses interconnected nanofiber spacing with sub-50 nm pores. The hierarchically porous architecture and strong crosslinking endow HANF-AF with a synergy of tensile strength up to 83.1 MPa and thermal conductivity down to 22.0 mW·m-1·K-1. Their robustness enables knitting into an industrial-grade textile with superior insulating features over conventional thermal insulating fibers. By leveraging ion-mediated hierarchical assembly of recycled nano-building blocks, this work establishes a scalable and sustainable strategy for engineering multifunctional nanofibrous architectures, offering a blueprint for creating next-generation flexible, durable, and superinsulating materials for advanced thermal management.

Introduction
Clothing acts as a ‘second skin’ and plays an indispensable role in thermoregulation of the human body by maintaining a comfortable microclimate against temperature shocks1, 2. While traditional natural fibers have historically served this purpose, aerogel fibers (AFs), with their high porosity and ultralow thermal conductivity, and alignment with sustainable development targets, are attractive alternatives for personal thermal management3, 4. However, the advancement of AFs has been persistently hindered by a fundamental trade-off between mechanical strength and thermal insulation5. An increase in porosity, which is essential for insulation, inevitably results in an exponential decay in mechanical strength, posing roadblocks to their processing via industrial weaving or knitting3, 6, 7. Despite extensive efforts dedicated to enhancing fiber strength from tens of kilopascals (kPa) to approximately 70 MPa8-13, this is sufficient only for manual weaving and insufficient to meet the demands of complex textile engineering.

The fabrication of AFs typically involves a solution-based spinning process, wherein the sol-gel transition is a critical determinant for AFs formation14, 15. The sol-gel transition could instantaneously stabilize the nascent porous network, even within the fibrous 1D confined space, while simultaneously posing a challenge in controlling the interconnected fibril networks and across multiple length scales to effectively redistribute stress for maintaining mechanical robustness16, 17. At the molecular scales, the polymer chain units are the basic determinant for the AFs architecture. The rigid polymers with conjugated backbones, such as aramids, intrinsically contain inter- (e.g., hydrogen-bonding, π-stacking) and intramolecular (e.g., C-C, C=C) interactions to guarantee the exceptional strength (~ 30 GPa) and high modulus (theoretical Young’s modulus > 120 GPa), and thermal stability (limiting oxygen index >28)18-21. However, this dense, highly crystalline packing compromises in moderate thermal insulation and creates significant end-of-life challenges, as the robust interactions render conventional fibers notoriously difficult to recycle22. To address these dual challenges of performance and sustainability, a transformative strategy involves deconstructing waste aramid fibers into their nanoscale building blocks, aramid nanofibers (ANFs), and reassemble them into porous aerogel architectures. This approach not only enables a circular life cycle through material upcycling but also provides a versatile platform for unprecedented structural control. The resulting high-aspect-ratio ANFs, with their rich surface chemistry, can be engineered into form an interconnected nanoporous network for underpinning stress redistribution and enabling efficient axial stress transfer19-21. On the mesoscale, these nanofibrils organize into a continuous nano- and micro-meter-scale porous network, which governs both thermal insulations derived from entrapped stationary air, and macroscopic force distribution by transmitting macroscopic stress along percolating fibrillar23-25.

The spatial arrangement of the nanofibril building blocks fundamentally determines the mechanical load-transfer pathways, whereas the porosity, pore size, interconnectivity, and synergistically govern the thermal transport. This necessitates precise regulation of the building block interactions through synergistic control of the physicochemical surface properties (e.g., wetting, surface potential, and the noncovalent interaction forces)26-29 and kinetic external fields (e.g., electric/magnetic fields, solvent environment)30, 31 and post-treatment processes (e.g., freeze-casting, strain alignment, and salting out)15, 24, 32-34. Whether acting on simple building blocks or the products of interfaces, microstructures, and hierarchical porous gradients, these factors facilitate the formation of a robust network and its thermal insulation performance. Despite advances in fundamental design principles, the synergistic optimization of mechanical strength and thermal insulation in AFs, while simultaneously enabling scalable production, remains an open issue.

Herein, we present and validate a strategy for tuning the hierarchical structures of AFs via the use of recyclable heterocyclic aramid nanofibers (HANFs) as nanobuilding blocks. This strategy is compatible with industrial wet-spinning, enabling the fabrication of fibers with remarkable mechanical strength by controlling building blocks hierarchical assembly, which synergistically combines molecular engineering with charge modulation to coordinate surface potential and coacervation kinetics. The resulting hierarchical HANF-AF achieves both the desired thermal insulation (22.0 mW·m-1·K-1) and robust mechanical properties (tensile strength 83.1 MPa). Thermoregulatory textiles have been manufactured via a commercial automated knitting process to verify their industrial processability. The resulting knitted fabric provides a 5.1°C greater temperature difference than does its cotton counterpart. This work establishes a scalable and sustainable pathway that bridges molecular-level design with industrial manufacturing, accelerating the translation of high-performance thermally insulating fibers from laboratory innovations to market-ready applications.

Results
Fabrication of hierarchical HANF-AF and textile engineering
Fig.1a and Supplementary Movie 1 illustrate the wet-spinning process for hierarchical HANF-AF production, which encompasses extrusion, coagulation, washing/drafting, solvent exchange and supercritical drying conducted on a custom-built wet-spinning line. During the coagulation stage, the recyclable nanobuilding blocks of HANFs assemble into a hierarchical structure involving both a secondary assembly, including proton-mediated HANF nanofiber assembly and nonsolvent-induced phase separation (NIPS) (Fig.1b). As summarized in Fig.1c, the resulting HANF-AF demonstrates a superior combination of mechanical-porosity compared with state-of-the-art counterparts (Kevlar-ANF, polyimide and biomass) (Supplementary Data 1). They could achieve an unprecedentedly broad tunable range of tensile strengths of 30.4-133.1 MPa within a porosity range of 59.8-95.4%, through coagulation bath and drafting ratio regulation (Supplementary Fig.10 and Table 1).

To validate the scalability, we established a liter-scale HANF dope preparation facility to match kilogram-level HANF-AF production via continuous 50×, 100×, and 200×filament wet-spinning (Supplementary Figs. 8 and 9 and 11). The resulting 50-filament yarn (Fig.1d) exhibited exceptional flexibility and robustness, characterized by a tensile strength of 2.0 cN/dtex, a maximum breaking load of 12.4 N, an elongation at break of 16.2%, and an elastic modulus of 33.1 cN/dtex, while maintaining a single-fiber porosity of 84.3% and tensile strength of 84.7 MPa (Supplementary Fig.12). This desirable flexibility and mechanical robustness guarantee yarn processability on commercial automated knitting machines, where yarns are successfully knitted into large-area fabrics, ultimately sewn into a vest for further thermal insulation evaluation (Fig.1f, g). The resulting thermal vest provides a 5.4°C temperature gradient compared with that of its cotton counterpart (Fig.1h) at 0 ℃ environment temperature.

Recycling engineering of 3.4 nm HANF from waste aramid fibers
The top-down recycling strategy establishes a circular life cycle for aramid fiber by upcycling industrial waste and post-consumer materials into functional nanoscale building blocks, thereby addressing critical challenges in resource efficiency, waste management, and polymer recovery35, 36. As illustrated in Fig. 2a and Supplementary Fig. 13a, this closed-loop paradigm enables the direct regeneration of HANF spinning dopes from waste aramid resources and post-consumer aerogel textiles. These HANFs are subsequently harnessed to wet-spin into HANFs-AF and knit into useful textile. This approach delivers a sustainable and scalable strategy for manufacturing high-performance thermal insulation materials, which bridge the gap between sustainable polymer reprocessing and next-generation functional textiles development.

The exfoliation process is initiated by the anisotropic swelling of heterocyclic aramid microfibers upon immersion in the KOH/ dimethyl sulfoxide (DMSO) superbase system (Fig. 2b), which causes their diameter to expand from 14.1 μm to over 25.0 μm while retaining the nematic liquid-crystalline texture and progressively disintegrating into micrometer-scale fibril aggregates (Supplementary Figs.6 and 7). This structural breakdown driven at the molecular level by the infiltration of DMSO and hydroxide ions35, which disrupt the dense intermolecular H-bonding network, yields a complete dispersion of individual, negatively charged HANFs (Supplementary Fig.3). Notably, the unique molecular architecture of the heterocyclic aramid of the N-H bond dissociation energy of the benzimidazole group (82.4 kcal mol-1) is significantly lower than that of the amide group (91.4 kcal mol-1), rendering it more susceptible to deprotonation by the superbase (Supplementary Figs. 1 and 3). The as-prepared HANFs demonstrated an ultrafine morphology with an average width of 3.4 ± 0.9 nm (Fig.2c, d, and Supplementary Fig.14). This dimension is substantially finer than that of conventionally produced Kevlar aramid nanofibers (ANFs) (18.4 ± 5.5 nm)37 and approaches the width of a single heterocyclic aramid (Poly (p-phenylene-benzimidazole-terephthalamide, PBIA) molecular chain (0.5 ± 0.2 nm).

HANF secondary assembly
The intrinsic features of the nanobuilding blocks, coupled with the characteristics of the junction between them (e.g., entanglements, H-bonds), are the determinants of the mechanical and thermal-insulating performance of the final HANF-AF. As schematically illustrated in Fig.3a, the dimensional variations among the PBIA polymer chains, HANF and Kevlar-ANF exhibited a significant size effect on the assembly process (Supplementary Figs.15 and 16). The ultrafine HANFs not only provide abundant active interfaces for network formation, but also establish a versatile material platform for precise structural engineering across nano-, micro-, and macroscopic scales38.

HANF assembly is dictated by a balance between noncovalent interactions (H-bonding, π-π stacking, van der Waals) and electrostatic repulsion, both of which originate from the charged states of the amide and imidazole groups (Supplementary Figs.3 and 20). These groups exhibit distinct protonation kinetics37, 39, 40, enabling the programmed stepwise assembly. As illustrated in Fig.3b the formation of complex hierarchical structures arises from HANF assembly, which is governed by proton-triggered synergistic Coulombic attenuating forces and noncovalent interactions, proceeding via a two-stage pathway. First, ultrafine nanofibers coalesce laterally to form nanofibril bundles. Subsequently, these nascent nanobundles undergo further micellar condensation, progressively maturing into assemblies. The Coulombic interactions, quantified by the Zeta potential (ζ), govern the separated distances26. Within the KOH/DMSO superbase system, HANFs achieve exceptional electrostatic stabilization via strong negatively charged inter-fibril repulsion (ζ=-46.1 mV). The introduction of an acidic coagulant dramatically modulates these interactions. As the proton (H⁺) concentration increases, the negative surface charge on HANF is progressively neutralized (Supplementary Fig.17). As depicted in Fig.3c, this process leads to significant Zeta potential reduction with a critical point of pH~11.5 (ζ=-14.3 mV), which attenuates the repulsive Coulombic barrier, thereby initiating the bundling of HANFs.

In particular, proton introduction-triggered H-bonding reconstruction is attributed to the preferential protonation of high-pKa amide groups over imidazole groups, as spectroscopically evidenced by the progressive intensification of the amide II (1537 cm-1) and amide I (1658 cm-1) bands depicted in the FT-IR spectra (Supplementary Figs.18b and 18c). The increase in the characteristic peak at 1257 cm-1, assigned to the imidazole N-H bond, subsequently signals the onset of the second protonation stage, which drive the coalescence of nanofibrils (Supplementary Fig.18d). This two-stage transition upon protonation was further corroborated by UV-vis spectroscopy, which revealed a progressive blueshift of the absorption peak from 420 nm (deprotonated state) to 360 nm (aggregated state) (Fig.3d and Supplementary Fig.19).

The protonation of charged amide/imidazole groups (H⁺+-N⁻-→-NH-) is an exothermic process driven by a favorable enthalpy change. Concurrently, a multitude of noncovalent interactions (Supplementary Fig.19) push the neutralized nanofibers into interfacial regions, facilitating the formation of aggregate structures. Linearized Cloud Point (LCP)41 calculations and the experimental phase diagram (Supplementary Figs.21 and 22) confirm that the proton-triggered assembly of HANF is an effective excess enthalpy process. This acid-accelerated phase separation is explicitly summarized in the HANF-DMSO-H2O ternary phase diagram (Fig.3e). As the acidity increases, the binodal curve, defined by the cloud-point, shifts towards the HANF-DMSO binary axis, reflecting the reduced nonsolvent or equivalently, an elevated nanofiber concentration required to initiate phase separation. For example, in a 2 wt% HANF dispersion, acidification of nonsolvent reduces the phase separation threshold from 30 vol% (pure water) to 16 vol% (2 wt% aqueous acid solution), demonstrating the critical role of acidity in modulating the thermodynamic boundaries of phase separation.

The acid-triggered microstructural evolution of HANF aggregates further drives significant macroscopic rheological transitions. As shown in Fig.3f and Supplementary Fig.23, the zero-shear viscosity surges from 3.4 Pa·s to 29.5 Pa·s (8.4-fold increase) at the critical gelation threshold (0.5 wt% acid), indicating progressive an inter-nanofiber crosslinking and percolating network. To bridge the molecular-level interactions with this multi-scale assembly, and to visualize the underlying assembly dynamics, we performed coarse-grained molecular dynamics (CG-MD) simulations. In simulations modeling the experimental protonation assembly, we progressively reduced the negative charge on nanofiber beads, directly mimicking the attenuation of electrostatic repulsion (quantified by Zeta potential as high, moderate, and low, Fig. 3g). These simulations provide compelling visual confirmation of gelation (Fig. 3g and Supplementary Figs. 24-27), revealing that reduced Coulombic repulsion triggers nanofibers coalescence into denser aggregates (driven by short-range attractions) while expanding inter-aggregate voids. This simulated aggregation provides a direct mesoscopic snapshot that connects the molecular-level H-bond reconstruction (FT-IR) and electronic transitions (UV-vis) to the macroscopic thermodynamic changes (phase diagram, Fig. 3d and 3e) and gelation (rheology, Fig. 3f). Collectively, spectroscopy, zeta potential, phase mapping, rheology, and CG-MD simulations form a cohesive, multi-scale framework. This demonstrates that modulating electrostatic barriers through protonation kinetics deterministically controls coagulation dynamics and hierarchical pore architecture, enabling precise microstructural engineering of HANF-AFs. Collectively, these results demonstrate that modulating electrostatic barriers via protonation kinetics deterministically controls coagulation dynamics and hierarchical pore architecture, thereby enabling microstructural engineering of HANF-AF.

HANF-AFs hierarchical architectures and thermal-mechanical performance
To elucidate the dynamic phase evolution and hierarchical architecture formation within the one-dimensional confinement of a spinning filament, we employed in-situ polarized optical microscopy (POM) coupled with high-speed imaging (Supplementary Fig.28). As depicted in Fig.4a, the NIPS initiates at the extrudate surface, where steep coagulant/solvent concentration gradients drive rapid solidification, forming a continuous semi-permeable skin layer. Time-resolved POM images demonstrate birefringent gelation fronts propagating radially inwards from this skin layer toward the isotropic core, until the structure develops and matures. In addition, the solidification front propagation speed is proportional to acid concentration in the coagulation bath (Supplementary Figs.29 and 30). As summarized in Fig.4b, the extrusion filament gelation rate in a 10 wt% acid coagulation bath is 1.8 times faster than that in a 2 wt% acid bath.

The porous architecture of HANF-AFn (n denotes acid identity/concentration) is engineered through a synergistic interplay of thermodynamic/kinetic control (Supplementary Figs.31-33) and mechanical drafting, with bath acidity acting as a variable governing nanofibril bundling and hierarchical assembly (Supplementary Figs.34 and 35). Modulating coagulation bath acidity serves as a key control parameter, where the introduction of protons suppresses elastocapillary thinning and internal stress of the aggregate network through attenuating the electrostatic repulsion rate (Supplementary Fig.36)42, yielding expanded fiber diameters and elevated elaborate porosity (Supplementary Fig.40). Fundamentally, this high performance is rooted in the selection of heterocyclic aramid nanofibers (HANFs), which proved to be a superior nanobuilding block compared to conventional Kevlar- and meta-aramid nanofibers for achieving both high strength and high porosity (Supplementary Fig. 39 and Note 2). This transition increases the total porosity from 56.3% (HANF-AFH2O) to 95.4% (HANF-AF2wt%H2SO4, Supplementary Fig.36c). As depicted in Fig.4c, HANF-AF2wt%H2SO4 exhibited a radially skin-shell-core graded porous architecture, where each hierarchical layer presented distinct mechanical and thermal features. This architecture contains gradient macropores (0.5-5 μm) within the shell layer and a fine nanoporous structure (3-50 nm) that constitutes the solid matrix of both the macropore walls and the core layer, as confirmed by mercury intrusion porosimetry (Supplementary Figs. 38, 40-43).

Fracture failure analysis (SEM images in Supplementary Fig.45) reveals fibril pull-out toughening in core and skin regions, where protruding the intrinsic high strength of nanofibrils43. In-situ compression and nanoindentation (Supplementary Figs.46 and 47) validate enhanced load-transfer efficiency in the core microstructure. As a result, HANF-AF achieves a superior strength-porosity balancing feature (Fig.1c and Supplementary Figs.10 and 48, detailed parameters in Supplementary Data 2 and Supplementary Table 3), which is attributed to the uniform hierarchically porous structure and synergistic dense-packed aligned structure with a continuous uniform nanoporous core structure. In addition, the drafting also enables microstructural alignment, which confers substantial mechanical reinforcement. The drafted AF2wt%H2SO4 mixture achieves a tensile strength of 111.2 MPa, representing a 271% enhancement over its undrawn counterparts (30.4 MPa, Fig.4d and Supplementary Figs .49 and 50, and Table 1). Beyond these impressive static properties, the fibers exhibit excellent dynamic performance critical for textile applications. They demonstrate outstanding fatigue resistance, robustly withstanding 5,000 cycles of both severe 180° bending and high-stress tensile loading with negligible degradation (Supplementary Fig. 51).

To elucidate the reinforcement mechanisms by hierarchical architecture and nanofiber orientation, we perform a simulation to analyze non-covalent forces (e.g., slippage, pull-out) during the fracture process with 3D Timoshenko beam-element chains representing individual nanofibers (Supplementary Figs.52-54). Three architecturally distinct models with the assigned consistent porosity and density have been built with the characteristics of isotropic network, aligned network, and aligned-hierarchical network, respectively (Fig.4e). Progressive microstructural reorganization, such as nanofiber straightening, reorientation, and pore compression, gradually emerged accompanied by the sequential deformation (Supplementary Fig.55). As depicted in Fig.4f, at 20% tensile strain, the ‘aligned-hierarchical’ fiber demonstrated uniform force distribution with enhanced stress transfer efficiency between nanofibers compared with ‘isotropic’ and only ‘aligned’ counterparts. Critically, the hierarchical architecture facilitated macropore-wall densification, increasing load-bearing capability (Supplementary Fig.56). Thus, synergistic contributions from enhanced interfibrillar interactions, optimized nanofiber orientation, and hierarchical structural assembly collectively govern the macroscopic tensile performance.

The exceptional thermal insulation of HANF-AFs originates from their precisely engineered hierarchical porosity (Fig. 4g), which traps stationary air with closed macropores (2 μm) and nanopores (sub-50 nm)23. Crucially, the fine and dense nanopores have dimensions smaller than the mean free path of air molecules (~70 nm)25, inducing a Knudsen diffusion regime that suppresses gaseous conduction and convection. Concurrently, the macro-porous cellular shell compartmentalizes air into semi-enclosed cells, thereby suppressing large-scale convective loops. Furthermore, solid phase thermal conduction is minimized through interfacial phonon scattering within the ultrafine (3.4 nm) nanofibrillar network and the elongation of heat transfer pathways. The hierarchical architecture also functions as an intrinsic and efficient radiation barrier, effectively attenuating thermal radiation (Supplementary Fig. 60)3, 44-46. Therefore, this exceptional insulating performance arises not from a single mechanism but from the synergistic suppression of all four heat transfer modes—gas conduction, solid conduction, convection, and radiation—enabled by the hierarchical design. This integrated approach achieves a remarkably low thermal conductivity of 22.0 mW·m-1·K-1 with a porosity of 89.1%. Infrared thermography confirmed superior thermal resistance (Fig.4h and Supplementary Figs.57 and 58) that a single-layer HANF-AF mat (120 μm) achieved 5.9 μm/K on a 100°C substrate, outperforming for Kevlar-ANF-AF (9.9 μm/K), despite a larger fiber diameter (180 μm) and higher porosity (96.7%) (Supplementary Figs. 39f and 59). Fig.4i further highlights the exceptional thermomechanical performance of HANF-AFs, exhibiting a thermal conductivity of 22.0-65.5 mW·m-1·K-1 and tensile strength of 30.4-133.1 MPa, surpassing traditional thermal-insulating fibers (SiO2, cellulose, silk) and synthetic aerogel fibers (PBO, polyimide) (Supplementary Table 1 and Supplementary Data 1).

Wearable textile engineering and multifunctional thermal management
The successful industrial-scale knitting of HANF-AF represents a critical milestone towards personal thermal management, as conventional aerogels typically suffer from fragility and poor bendability, which can cause catastrophic fracture during yarn, textile and fabric preparation. As demonstrated in Fig.5a, the current HANF-AF yarn enables continuous processing of commercial flat knitting machinery without mechanical failure. The batch-produced HANF-AF yarn (containing 50-filaments) exhibited a breaking load exceeding 12 N (Supplementary Fig.12), substantially surpassing the ~3.4 N threshold required for industrial knitting machinery. A series of joint vests with splicing a HANF-AF fabric (left) and a counterpart fabric (right) have been fabricated directly from yarn via a programmed knitting process (Supplementary Figs.61 and 62, and Movie 2). The knitted HANF-AF textile exhibited a uniform and smooth texture (Fig.5b) and with excellent mechanical flexibility, was capable of withstand extreme deformation, such as 180° twisting and folding (Supplementary Fig.63). The float-plated HANF-AF fabric with a minimal thickness of 0.82 mm, exhibits a thermal conductivity of 43.5 ± 1.2 mW·m-1·K-1, which is significantly inferior to polyimide (75.1 mW·m-1·K-1), aramid (64.3 mW·m-1·K-1), silk (72.7 mW·m-1·K-1), cotton (66.3 mW·m-1·K-1), and polyester (93.7 mW·m-1·K-1) (Supplementary Figs.64-66 and Table 2 and Movie 3). This value is higher than that of a single fiber, primarily due to convective heat transfer within the fabric’s macroscopic pores47. Nevertheless, the knitted architecture was deliberately selected for its unique advantages in wearable thermal management. The interlooping structure provides critical flexibility and resilience, while simultaneously trapping a substantial layer of static air to enhance the overall breathable and insulation performance of the garment48.

Afterwards, as displayed in Fig.5c, the joint vest thermal management performance was evaluated using a thermal manikin system in a 0°C environmental chamber. The HANF-AF side demonstrated superior insulation performance, characterized by maintaining a higher manikin skin temperature (32.7 °C for HANF-AF vs. 31.3 °C for cotton). As depicted in the infrared thermography of Fig.5c and the summary curve in Fig.5e, the HANF-AF fabric (0.037 g cm-2 areal density) exhibited a spatial thermal uniformity with stabilized outer surface temperatures averaging 11.1°C, maintaining a large temperature gradient of 21.6°C relative to the manikin skin, even after maintaining 20 min (Supplementary Movie 4). This represents a 5.1°C greater temperature difference than that of cotton fabric with the consistent condition. The infrared thermograph in Fig.5d further proved that the conventional aramid, silk, and polyester fabrics depicted inferior thermal insulation properties with stable outer surface temperatures of 18.8, 18.3, and 19.4 °C, respectively, even with a higher areal density of 0.059-0.065 g cm-2 (Supplementary Table 2).

To validate the thermal insulation capability of the HANF-AF fabric, field testing was performed under real winter conditions (-2.2°C, 3.0 km/h, gentle breeze, zero solar irradiation). A volunteer wore the splicing thermal vest, comprising HANF-AF fabric and cotton fabric on the counter side (Fig.5f and Supplementary Fig.68 and Movie 5). Time-resolved infrared thermography revealed that a distinct delay in thermal equilibration for the HANF-AF side (80.7 s) compared to cotton (45.5 s). At steady state, the HANF-AF exterior surface maintained a 3.1°C lower temperature than cotton, confirming reduced thermal dissipation. Upon removing the vest, the infrared analysis further revealed >1.7°C higher skin temperature beneath the HANF-AF section versus the cotton-covered range. The HANF-AF fabric exhibits exceptional thermal durability, maintaining over 97% of its original insulating capability after undergoing repeated thermal cycling between 100 °C and -196 °C (Supplementary Fig. 70). This resilience highlights its reliability for applications in subject to extreme and dynamic temperature fluctuations. Furthermore, after encapsulation of HANF-AF within thermoplastic polyurethane (TPU), stable water repellency and thermal insulation were achieved (Supplementary Figs. 69, 71 and 72), establishing a foundation for next-generation machine-washable thermal insulating textiles.

Methods
Chemicals and resources
The waste heterocyclic aramid fibers were procured from China Bluestar Chengrand Co., Ltd. Dimethylsulfoxide (DMSO, 99.7%), Na2CO3, and KOH were purchased from the Aladdin Chemical Reagent Co., Ltd. (Shanghai, China). Ethanol (> 99.5%), tert-butanol, hydrochloric acid, sulfuric acid, acetic acid, and phosphoric acid were all obtained from Adams-beta Co., Ltd (Shanghai, China). Deionized water was produced using a Millipore water purification system.

Preparation of HANF spinning dopes
To prepare the nanofiber spinning dope, waste aramid fibers are washed, chopped, pre-dissolution in a superbase (DMSO/KOH) solvent system, stirred, and filtration. Initially, waste aramid fibers were boiled in 0.2 M Na2CO3 solution for 30 minutes, followed by washing with purified water three times. Subsequently, the dried, chopped aramid fibers (0.5-1.0 cm) were added to 2 L of dimethyl sulfoxide (DMSO) containing 1.5 wt% KOH and 2.0 wt% water. This mixture underwent 24 hours of pre-dissolution and 24 hours of magnetic stirring at room temperature, yielding a dark red, viscous dispersion of heterocyclic aramid nanofibers (HANF). Finally, the dark red dispersion was filtered to obtain the homogeneous spinning dopes. These dopes remained stable, exhibiting no agglomeration and flocculation, attributed to the deprotonation and electrostatic repulsion between the nanofibers.

Preparation of HANF-AF
HANF-AFs were prepared via a wet-spinning process. A 2 wt% HANF spinning dope was extruded into an aqueous acid coagulation bath. Upon coagulation, indicated by a color transition of the nascent filaments from dark brown to pale yellow, the filaments were washed, draft in a secondary bath, and wound as hydrogel fibers. The resulting hydrogel fibers were first aged in deionized water to remove residual acid and DMSO, followed by immersion in a 25wt% aqueous tert-butanol solution for 12 hours. Finally, the hydrogel fibers were frozen in liquid nitrogen and lyophilized at -44.5 °C and 0.120 mbar (Labconco) to produce the final aerogel fibers. Unless otherwise specified, all characterizations were performed on these freeze-dried samples.

For scalable fabrication, multifilament and weavable yarns were prepared via a supercritical drying process. Key spinning parameters included a spinneret with 50 holes (Φ0.25 mm each), a coagulation bath of 2wt% H2SO4 aqueous, and a draft ratio of 1.3. The collected hydrogel fibers were subjected to three solvent exchange cycles in anhydrous ethanol before being supercritically dried at 35 °C and 9.5 MPa for 12 hours.

Characterization and measurement
Chemical structures were recorded using Fourier-transform infrared (FTIR) spectrometer (Thermo Scientific, Germany) and Raman spectrum (LabRANM Odyssey, Horiba) with a 633 nm laser excitation. Nanofiber surface morphology was measured by atomic force microscopy (AFM, Dimension ICON, Bruker, Germany). Samples for AFM were prepared by depositing a 5 μL droplet of an ultra-dilute HANF suspension (0.00005 wt% in ethanol) onto a freshly cleaved silicon wafer (1×1 cm), followed by air drying. The zeta potential of diluted HANF dispersions was measured using a Zetasizer (Malvern, UK). The measurements were performed on HANF dispersions diluted to 1.0 mg/mL in a DMSO solution to ensure accurate readings. Optical properties, including the transmittance for cloud point determination and UV-vis absorption spectra, were recorded on a UV-VIS-NIR spectrometer (Perkin Elmer Lambda 950, America). For titration experiments, a 0.125 wt% HANF dispersion was used, and the acidic titrant was pre-diluted in DMSO to prevent rapid, localized aggregation. The residual DMSO content in aqueous solutions was quantified by high-performance liquid chromatography-mass spectrometry (HPLC-MS, LC-30AD-8050 MS, Japan). Rheological properties of the spinning dopes were characterized over a shear rate range of 0.1 to 1000 s-1 using a rheometer (TA Instruments DHR-2, American) with a parallel-plate geometry. The in-situ dynamics of double diffusion and the formation of liquid crystalline structures in precursor HANF fibers under acidic coagulation bath were recorded using an optical microscope (Nikon Eclipse) equipped with a high-speed camera (AMETEK, MIRO C321, American) operating at 200-2000 fps.

The cross-section morphology and porous nanoscale architecture of the fibers were examined using field-emission scanning electron microscopy (FESEM, Regulus8220, JEOL, Japan) at an accelerating voltage of 10 kV. Structural characterization at the nanoscale was performed at the Shanghai Synchrotron Radiation Facility, where wide-angle X-ray diffraction (WAXD) patterns were collected. Mechanical properties of single filaments were assessed using a universal testing machine (CMT6103) equipped with a 5 N load sensor. The specific surface area and pore size distribution of the aerogel fibers were determined by N2 adsorption-desorption isotherms using a Brunauer-Emmett-Teller (BET) analyzer (ASAP 2020, USA) and mercury intrusion porosimetry (Autopore IV 9500, USA). Tensile tests of single fibers were conducted with a 1 cm gauge length at a strain rate of 1 mm/min, and all reported values represent the average of at least seven independent measurements. Mechanical strength of the aerogel fibers yarn was evaluated using an MTS Exceed Model E43 machine with yarns of 62 T/m twist and 17 cm length. Indentation experiments were conducted along the fiber axis at a constant loading rate of 0.08 μm/s in a custom-made in situ nanomechanical instrument (SEMentor) with a 5-μm-diameter flat conical diamond indenter tip.

To measure the thermal conductivity of the HANF-AF, we prepared a HANF foam with a similar aligned porous structure for estimation. The thermal conductivity (λ) of the fabrics was measured using the transient plane source method with a thermal constant analyzer (TPS 2500 S, Hot Disk, Sweden) under heating power of 5 mW and heating time of 10 s. In detail, the Kapton probe (type 7281) was placed in the middle of two pieces of fabric, and a certain pressure was applied above the fabric, followed by stabilization for 60 min to start the test. Thermal imaging and temperature mapping were performed using a high-resolution thermal camera (FLIR Systems Inc., A700, America).

Fabrication of knitted textiles
The interlooping architecture of knitted fabrics imparts inherent extensibility and three-dimensional conformability, which can effectively mitigate mechanical damage to brittle aerogel fibers and enhance the volume of entrapped static air layer, thereby improving thermal insulation. However, high-speed knitting imposes significant stress on yarns as they pass through tensioners, feeders, and are rapidly formed into loops by needles, often leading to catastrophic fiber failure. Such failures result in processing interruptions and critical fabric defects, including uneven loop sizes, dropped stitches, and holes. Our batch produced aerogel fiber yarn, exhibiting a breaking load exceeding 12.0 N, comfortably met the tensile requirements for low-speed operation of the commercial flat knitting machine (Stoll CMS 530, 7.2-gauge), which operates at 3.4-5.0 N. To visualize the knitting process and details of the HANF-AF yarn, clear footage of the knitting procedure was captured using a flat knitting machine (SWG061N2, Shimajima Seiki Co., Ltd., Kochi).

The overall process involved: establishing the knitted fabric structure, designing the garment pattern, inputting and applying knitted machine design parameters, fabricating the knitted fabric swatches, and integrating zipper closures at the shoulder, side waist, and center front locations (Fig.5a). A vest garment was designed and fabricated for adult males with a height of 180 cm. To minimize stress on the yarn, a float-plated fleecy stitch structure was selected, wherein the aerogel fibers served as the fleecy yarn and a commercial aramid fiber was used as the ground yarn. For consistent comparison, control fabrics from silk, cotton, aramid, and polyester yarns were also prepared using the identical knitted structure. Finally, the resulting fabric swatches were integrated via zipper stitching to produce a bipartite insulated vest for thermal performance evaluation.

Warm manikin system test
The thermal insulation performance of the fabrics was evaluated using a thermal manikin system (Thermetrics, America). All tests were conducted within a climatic chamber maintained at 0 °C to simulate a cold environment. The manikin, featuring multiple independently heated zones to ensure a uniform surface temperature, was maintained at a constant 35.0 °C. For each test, the manikin was first outfitted with a standard base layer of clothing (trousers, socks, shoes, and a hat) before the insulated vest was donned. The entire assembly was allowed to reach a thermal steady state, at which point a thermal camera was used to record the temperature distribution across the vest's outer surface.

On-body thermal-insulation test
To validate the heat retention capability of the HANF-AF fabric in a practical scenario, a field test was conducted under cold winter conditions in Beijing, China. The ambient environment was maintained at -2 °C with a gentle breeze of approximately 3 km/h and an absence of solar irradiation. A volunteer wore the custom-fabricated bipartite vest, and the evolution of the external surface temperatures was monitored using a thermal camera. As the study protocol was non-invasive, ethics oversight was waived. The research participant provided signed informed consent to participate in the study and to have their images and movies published.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript reports the development of knittable, thermally insulating, and sustainable aerogel fibers (HANF-AFs) derived from recyclable heterocyclic aramid nanofibers (HANFs). Through an ion-mediated assembly strategy, the authors successfully engineer a hierarchical porous architecture that overcomes the conventional trade-off between mechanical robustness and thermal insulation. The resulting fibers exhibit outstanding tensile strength along with ultralow thermal conductivity. Moreover, the authors demonstrate a practical and scalable route from single-fiber fabrication to automated textile manufacturing. Overall, this work is both innovative and thorough. Before recommending publication in Nature Communi., I suggest minor revisions to further clarify the key contributions and strengthen the manuscript.\n1. To fully substantiate the \"closed-loop\" recycling claim in Figure 2a, could the authors provide direct evidence? For example, can the final aerogel fiber/textile be reprocessed back into new aerogel fibers?\n2. The term “multi-scale” is used for structure, pores, and the model of fiber. In the reviewers' view, Supplementary Figure 15 does not constitute a multi-scale model. The authors should ensure consistency and clarity in their terminology throughout the manuscript.\n3. The manuscript mentions “three wet-spinning strategies.” Could the authors provide evidence that directly correlates each one to the resulting fiber porosity and strength?\n4. While the mechanical improvement of drawn fibers is clear, direct structural evidence for alignment is missing. Could the authors provide a quantitative orientation factor to confirm the increase in nanofiber alignment?\n5. In the discussion of Figure 4h, a direct comparison of the temperature difference (ΔT) can be misleading without accounting for thickness. The authors should report and compare the normalizes for thickness (R = thickness / ΔT).\n6. For the Kevlar-ANF-AF control sample used in Figure 4h, could the authors provide its preparation method and key characterization data (e.g., fiber diameter, porosity, microstructure) to validate the comparison?\n7. There is a notable difference between the thermal conductivity of a single fiber (22.0 mW·m-1·K-1) and the final knitted fabric (43.5 mW·m-1·K-1). While this is expected, a more detailed discussion is needed. Could the authors please elaborate on why the knitted structure was chosen and the factors influencing its thermal resistance?", "reviewer_2": "The manuscript entitled “Knittable, thermally insulating, and sustainable aerogel fibers enabled by ion-mediated hierarchical assembly” by Gang Xiao and co-workers presents a well-designed ion-mediated hierarchical assembly strategy for producing heterocyclic aramid aerogel fibers with both high mechanical strength and ultralow thermal conductivity. The study is notable by comprehensive multiscale characterization and the effective integration of simulations with experiments to elucidate the underlying mechanisms. While the approach effectively addresses the trade-off between mechanical robustness and thermal insulation in aerogel fibers, several aspects require further improvement before the manuscript can be recommended for publication:\n1) The Introduction should be revised to provide a clearer comparative framework between traditional aramid fibers and the proposed aerogel fibers, particularly in terms of performance and sustainability. This will help highlight the main advances: improved structural controllability and end-of-life recyclability.\n2) The stability of the fibers under operational conditions such as mechanical fatigue and humid aging should be verified.\n3) The comparative analysis should be expanded to include common high-performance insulating fibers such as aramid and PI. For a fair evaluation, the thermal and mechanical properties should be compared at the same areal density or thickness.\n4) The connection between the CG-MD simulations and the experimental data should be strengthened. We recommend directly relating the simulation results to measurements such as zeta potential and FT-IR spectra to provide a clearer basis for the proposed hierarchical assembly mechanism.\n5) The analysis of the thermal conduction mechanisms, although noting effects such as phonon scattering, would benefit from a more systematic theoretical treatment. Quantifying the contribution of these effects or comparing the measured conductivity with established models would provide a clearer and more rigorous validation of the proposed mechanisms.\n6) Given cost considerations, aramid aerogel fibers are mainly suited for high-end applications such as aerospace and specialized firefighting protection. These environments often involve dynamic, non-isothermal conditions. It would therefore be useful to include data on the fibers’ thermal insulation performance under dynamic temperature cycling\n7) It is noted that scaling up the wet-spinning process requires substantial use of the key solvent DMSO, despite the manuscript highlighting process recyclability. The authors should clarify how DMSO is handled during post-processing and whether its high consumption affects the overall sustainability and cost-effectiveness of the proposed strategy.\n8) For practical applications, the wash durability of the fabric should be addressed. It would also be useful to report whether the performance of the aerogel fibers has been tested under high-humidity conditions, along with data on microstructural changes and thermal conductivity.", "reviewer_3": "Zhang et al. report the fabrication of aerogel fibers derived from heterocyclic aramid nanofibers through an ion‑mediated hierarchical assembly strategy. The resulting fibers exhibit a dual‑scale porous architecture, combining a nanoporous core with a macroporous cellular shell, which enables the simultaneous achievement of exceptional tensile strength and ultralow thermal conductivity. Notably, the authors demonstrate a scalable fabrication route, including automated knitting, highlighting strong application potential for thermal‑insulating textiles. The experiments are well-designed, supported by extensive characterization. I recommend the potential acceptance after minor revision.\nDetailed comments are provided below:\n1. The authors should clarify the appropriateness of using the term “aerogel fibers.” The concept of “aerogel” is often loosely or inconsistently used in the literature. Although the IUPAC definition implies microporous structures with pore sizes below 2 nm, even classical silica aerogels typically exhibit pores of 10–50 nm (https://doi.org/10.1002/adma.202001839). In this work, the pore sizes of the fibers are clearly larger than these commonly accepted ranges. The authors should therefore explain why the material is categorized as an aerogel rather than a foam or another type of porous fiber, and justify the terminology based on structural features, functional behavior, or prevailing conventions in aerogel research.\n2. The manuscript suggests a strong mechanical‑thermal contradiction in aerogel fibers; however, the achievable performance range in related systems should be accurately reflected. For example, in the cellulose‑based aerogel fiber, tensile strengths as high as 71.83 MPa coupled with thermal conductivities as low as 0.023 W m-1 K-1 have been reported (https://doi.org/10.1021/acs.nanolett.1c03943). The authors are encouraged to incorporate such representative data into the Introduction and adjust the comparative analysis in Figure 1c accordingly, ensuring a fair and comprehensive contextualization of the performance landscape.\n3. The Kevlar‑ANF images in Figure 2d appear similar to those published in previous studies. If these images are reproduced, adapted, or modified from earlier literature, the original sources must be explicitly cited either in the figure caption or in the main text to ensure proper attribution.\n4. The manuscript should offer more detailed descriptions of key experimental procedures, particularly those related to the acquisition of UV–vis spectra, zeta‑potential measurements, and the AFM characterization of HANFs. Providing these details is essential for ensuring reproducibility and enabling readers to accurately assess the methodology.\n5. The manuscript introduces three programmable wet‑spinning strategies aimed at tailoring the hierarchical pore structure of the aerogel fibers. However, direct experimental evidence demonstrating the structural impact of each strategy is limited. The authors are encouraged to include comparative SEM images and corresponding analysis to clearly illustrate how each process parameter modifies the final pore morphology.\n6. In Figure 1 and Supplementary Table 3, the literature comparison should be updated to include recent and comprehensive citations. A more complete benchmarking will better contextualize the significance of the reported performance metrics and highlight the advancement contributed by this work.\n7. Several figures and tables in the Supplementary Information—such as Figure S38 and Tables S4 and S5—are critical to the overall findings but are not mentioned in the main text. These elements should be explicitly cited and discussed to guide readers and ensure that the supporting data are properly integrated into the narrative.\n8. The authors may consider moving the entire Figure 2 to the Supplementary Information. At its current placement, Figure 2 provides limited essential data and interrupts the logical flow of the assembly/gelation discussion in the main text. Relocating it to the SI would help streamline the narrative while still allowing readers to access the detailed characterization if needed."}, "author_response": "Revision Summary\n1. According to Reviewer 1’s comment (Q1), we have experimentally validated the “closed-\nloop” recycling, adding direct evidence to Supplementary Information (Supplementary\nFig. 13a and related discussion on Page 6, Line 130).\n2. According to Reviewer 1’s comments (Q3 & Q4), we have provided clearer evidence for\nstructure-property relationships, including a systematic comparison of spinning strategies\n(Supplementary Fig.10) and quantitative orientation data from 2D-WAXD\n(Supplementary Fig. 49d).\n3. According to Reviewer 1’s comment (Q5), we have normalized the thermal insulation\ncomparison in Fig. 4h by using the temperature gradient. (Fig. 4h and related discussion\non Page 15, Lines 311-313).\n4. According to Reviewer 2’s comments (Q2 & Q8), we have evaluated the fiber’s\noperational stability, adding new data on mechanical fatigue, humidity resistance, and\nwash durability (Supplementary Figs. 51, 69, 71 and 72, and related discussion on Lines\n281-284, Page 14; Lines 371-374, Page 18).\n5. According to Reviewer 2’s comment (Q4), we have strengthened the link between CG-\nMD simulations and experiments, adding a more quantitative, hierarchical assembly\nanalysis (related discussion on Lines 217-229, Pages 10-11).\n6. According to Reviewer 2’s comment (Q3), we have expanded performance benchmarking\nto include PI and Aramid fabrics and provided a normalized comparison using thermal\nconductance (Supplementary Fig. 63 and Table 2 in Supporting Information, related\ndiscussion on Line 344, Page 17).\n7. According to Reviewer 2’s comment (Q5), we have provided a systematic analysis of\nthermal conduction mechanisms, revising the schematic to emphasize the architectural\nrole in heat transfer (Fig. 4g on Page 12, Line 234) and supporting this with detailed\ndiscussion and new experiments on radiation blocking (Supplementary Fig. 60 and related\ndiscussed on Pages 14-15, Lines 302-310).\n8. According to Reviewer 2’s comment (Q6), we have validated the material's performance\nunder dynamic thermal cycling (-196 °C to 200 °C) (Supplementary Fig. 70 and related\ndiscussed on Page 18, Lines 369-372).\n9. According to Reviewer 2’s comment (Q7), we have clarified process sustainability with a\nDMSO recovery schematic and a cost-benefit analysis showing ~76% savings\n(Supplementary Fig. 13b and Text 1 in Supporting Information).\n10. According to Reviewer 1 (Q6) and Reviewer 3’s (Q3) comments, we have provided full\n1\ncharacterization for the Kevlar-ANF control sample and added proper citation for\nrepresentative images (Supplementary Fig. 39f, Fig. 2d on Line 143, Page 7). According\nto Reviewer 3’s comments (Q2 & Q6), we have updated all literature comparisons in the\nAshby diagrams and Supplementary Table 3 with the latest high-impact publications (Fig.\n1c and Supplementary Table 3 added corresponding literature).\n11. According to Reviewer 3’s comment (Q4), we have added more detailed experimental\nprocedures for AFM, UV-vis, and Zeta potential measurements in the Methods section\n(Page 20, Lines 419-426).\n12. According to Reviewer 1 (Q2) and Reviewer 3 (Q1), we have refined key terminology\n(“multi-scale”, “aerogel fiber”) for consistency and accuracy (Page 13, Lines 269-271).\n13. According to Reviewer 3’s comment (Q7), we have ensured all supplementary figures are\nproperly cited and discussed in the main text, with examples on (Supplementary Fig. 39\nand related discussed on Page 13, Lines 262-265; Supplementary Table 4 and 5, and related\ndiscussed on Page 14, Line 276).\nBelow we respond point-by-point to each of the referees’ comments in detail and point out the\nplaces where we have revised the text of the manuscript.\nReviewer #1\nThis manuscript reports the development of knittable, thermally insulating, and sustainable\naerogel fibers (HANF-AFs) derived from recyclable heterocyclic aramid nanofibers (HANFs).\nThrough an ion-mediated assembly strategy, the authors successfully engineer a hierarchical\nporous architecture that overcomes the conventional trade-off between mechanical robustness\nand thermal insulation. The resulting fibers exhibit outstanding tensile strength along with\nultralow thermal conductivity. Moreover, the authors demonstrate a practical and scalable\nroute from single-fiber fabrication to automated textile manufacturing. Overall, this work is\nboth innovative and thorough. Before recommending publication in Nature Commun., I suggest\nminor revisions to further clarify the key contributions and strengthen the manuscript.\nOur response:\nWe are grateful to the reviewer for the thorough review and the highly positive comment.\nQ1: To fully substantiate the \"closed-loop\" recycling claim in Figure 2a, could the authors\nprovide direct evidence? For example, can the final aerogel fiber/textile be reprocessed back\ninto new aerogel fibers?\nOur response:\nWe thank the reviewer for this constructive suggestion. To address the reviewer’s concern, we\nhave performed the proposed experiment, to experimentally validate the “closed-loop” concept.\nThe final HANF-AF yarn was successfully redissolved in a DMSO/KOH solution to regenerate\na HANF spinning dope, which was then wet-spinning into second-generation aerogel fibers.\nCharacterization confirms that these recycled HANF-AFs retain the essential hierarchical\nporous architecture. This direct experimental evidence is now presented in Figure R1 to\nexplicitly substantiate our recycling claim.\nWe have added the closed-loop recycled HANF-AFs to Figure R1 as Supplementary Fig. 13a,\nand supplemented the relative details in the revised manuscript on Line 130, Page 6:\n“As illustrated in Fig. 2a and Supplementary Fig. 13a, this closed-loop paradigm enables the\ndirect regeneration of HANF spinning dopes from waste aramid resources and post-consumer\naerogel textiles.”\nsuccessful replication of hierarchical porous structures in secondary recycled HANF-AFs\nunderscores the robust recyclability and sustainable applications.\nQ2: The term “multi-scale” is used for structure, pores, and the model of fiber. In the reviewers'\nview, Supplementary Figure 15 does not constitute a multi-scale model. The authors should\nensure consistency and clarity in their terminology throughout the manuscript.\nOur response:\nWe appreciate the reviewer's attention to terminological precision. We agree that the term\n“multi-scale model” for Supplementary Figure 15 was an overstatement and that consistent use\nof “multi-scale” is critical. Thus, we have conducted a thorough review of the manuscript and\nrevised the terminology accordingly. The term “multi-scale” is now exclusively used to describe\nthe physical structure of the material, which genuinely spans multiple length scales, from\nmolecular chains (sub-nm) and nanofibers (nm) to nanopores (nm) and finally to the\nmacroscopic fiber (μm).\nIn the Supplementary Information for Supplementary Fig. 16, the term “multi-scale model” has\nbeen corrected to: “Schematic illustration of nanobuilding block properties dictate network\narchitecture.”, which more accurately describes its content. We believe these revisions ensure\nthat the term “multi-scale” is now used in a consistent, accurate, and justified manner\nthroughout the manuscript.\nQ3: The manuscript mentions “three wet-spinning strategies.” Could the authors provide\nevidence that directly correlates each one to the resulting fiber porosity and strength?\nOur response:\nWe thank the reviewer for this valuable suggestion to more clearly present the structure-\n4\nproperty relationships for the different spinning strategies. To directly address this concern, a\ncomprehensive figure has been organized to systematically compare the three different spinning\napproaches as shown in Figure R2 (supplemented as Supplementary Fig. 10 in the Supporting\nInformation). It provides a detail mechanism and structure for each strategy and the resulting\nfiber:\nFirst, representative SEM cross-sectional images are provided for fibers produced under each\ncondition in Figure R2a (Supplementary Fig. 10a). These images visually substantiate the\ndistinct microstructures, such as the transition from a uniform porous network to a densified\nstructure or a pronounced hierarchical architecture.\nSecond, a summary table in Figure R2c (Supplementary Fig. 10c) link each spinning protocol\nto its key performance metrics, specifically spinning dope, coagulation bath, porosity and\ntensile strength. The data clearly show increasing the coagulation bath acidity and pre-\nprotonated dope leads to higher porosity but lower initial strength. This consolidated\npresentation offers the clear and direct evidence requested, allowing for an immediate\ncomparison of each spinning strategy engineers a unique structural and mechanical signature\nin the final aerogel fiber.\nIn response to your comment, we have added the corresponding detail data of Figure R2a,\nR2c as Supplementary Fig. 10a, 10c, and supplemented the corresponding descriptions in the\nrevised Supplementary Information on Supplementary Fig. 10:\n“(a) Schematic description of the three strategies of preparation methods for aerogel fiber\nporous structures, with accompanying SEM cross-sectional micrographs revealing the achieved\nporous morphologies. (b) Ashby diagrams of ultimate tensile stress versus porosity of AF\nfiber…... (c) Comparative analysis of the porosity and mechanical strength of fibers produced\nby the three strategies.”\nfiber porous structures, with accompanying SEM cross-sectional micrographs revealing the\nachieved porous morphologies. (b) Ashby diagrams of….. (c) Comparative analysis of the\nporosity and mechanical strength of fibers produced by the three strategies.\nQ4: While the mechanical improvement of drawn fibers is clear, direct structural evidence for\nalignment is missing. Could the authors provide a quantitative orientation factor to confirm the\nincrease in nanofiber alignment?\nOur response:\nWe thank the reviewer for pointing out this critical issue related to the quantitative analysis of\nthe orientation of the resultant fibers.\nTo quantify the degree of orientation, the Herman's orientation factor (ƒ) was calculated from\nthe azimuthal intensity distribution of the 2D WAXD patterns for the nanofiber alignment\ninduced by drawing. The results indicate that the fiber orientation index increased from 0.51 to\n0.60 (as summarized in Figure R3, supplemented as Supplementary Fig. 49d) as the draft ratio\n6\nincreased from 1.1 to 1.6. This quantitative result provides strong and direct evidence that the\nmechanical stretching process effectively induced nanofiber orientation. This trend of enhanced\norientation is consistent with the microstructural changes observed via SEM and the increase\nin fiber tensile strength obtained from mechanical testing.\nFigure R3. (c) 2D-WAXD patterns and (d) the calculated degree of orientation. Mechanical\ntensile drafting within the secondary bath enables precise control over the alignment of fibrillar\nand pore architecture. (e) Stress-strain curves of fibers under different draft ratio. This\nmechanical reinforcement is a direct result of the enhanced nanofiber alignment induced by\ndrawing, as confirmed by 2D-WAXD. The Herman's orientation factor increased from ƒ = 0.51\nto ƒ = 0.59 as the draft ratio was raised from 1.1 to 1.6, a trend supported by both the WAXD\ndata and the increased fibril parallelism observed via SEM, providing quantitative evidence of\na more oriented internal structure.\nWe have added the corresponding reproducibility data to Figure R3 in Supplementary Fig. 49d,\nand supplemented the corresponding descriptions in the revised Supplementary Information:\n“This mechanical reinforcement is a direct result of the enhanced nanofiber alignment induced\nby drawing, as confirmed by 2D-WAXD. The Herman's orientation factor increased from ƒ =\n0.51 to ƒ = 0.60 as the draft ratio was raised from 1.1 to 1.6, a trend supported by both the\nWAXD data and the increased fibril parallelism observed via SEM, providing quantitative\nevidence of a more oriented internal structure.”\nQ5: In the discussion of Figure 4h, a direct comparison of the temperature difference (ΔT) can\nbe misleading without accounting for thickness. The authors should report and compare the\nnormalizes for thickness (R = thickness/ΔT).\nOur response:\nWe thank the reviewer for this crucial comment. A direct comparison of ΔT is indeed\ninsufficient without normalization. To provide a fair and meaningful comparison of thermal\n7\ninsulation performance, we have calculated the temperature gradient (thickness/ΔT) across the\nfiber mats (details refer to Ref.: Adv. Mater. 2025, 37, 2507289), which serves as a normalized\nmeasure of their insulating capability under the given test conditions.\nThe temperature gradients for both the HANF-AF and the Kevlar-ANF-AF mats on the 100 °C\nhot substrate was calculated (data from Fig. 4h). The HANF-AF mat exhibits a temperature\ngradient of 5.9 μm/K (calculated from 120 μm / 20.3 K). The Kevlar-ANF-AF mat shows a\nlower temperature gradient of 9.9 μm/K (calculated from 180 μm / 18.2 K). This normalized\ncomparison, showing a 40.4% lower temperature gradient for our HANF-AF, confirms its\nsuperior intrinsic insulating capability per unit thickness.\nThe main revisions in the revised manuscript are as follows:\n(i) Normalized thermal performance data have been added in the revised manuscript (Fig. 4h)\non Line 234, Page 12.\n(ii) The revised manuscript discussion of Fig. 4h has been revised on Lines 311-313, Page 15:\n“Infrared thermography confirmed superior thermal resistance (Fig.4h and Supplementary\nFigs.57 and 58) that a single-layer HANF-AF mat (120 μm) achieved 5.9 μm/K on a 100°C\nsubstrate, outperforming for Kevlar-ANF-AF (9.9 μm/K), despite a larger fiber diameter (180\nμm) and higher porosity (96.7%) (Supplementary Figs. 39f and 59).”\nQ6: For the Kevlar-ANF-AF control sample used in Figure 4h, could the authors provide its\npreparation method and key characterization data (e.g., fiber diameter, porosity, microstructure)\nto validate the comparison?\nOur response:\nWe thank the reviewer for requesting this important information to ensure the validity of our\ncontrol experiment. To provide a comprehensive characterization of the Kevlar-ANF-AF\ncontrol sample, we have added detailed preparation methods and key performance data to the\nSupplementary Information.\nPreparation method: The Kevlar-ANF-AF was fabricated using a process analogous to that\nof our HANF-AFs to ensure a fair comparison. Specifically, a 2wt% Kevlar aramid nanofiber\n(ANF) dispersion, prepared by exfoliating Kevlar fibers in a DMSO/2wt% KOH solution, was\nwet-spinning into a 2 wt% H SO coagulation bath, followed by freeze-drying.\n2 4\nCharacterization data: The resulting control fibers exhibit characteristics consistent with\nthose reported for state-of-the-art Kevlar aerogel fibers in the literature (Ref.: ACS Nano 2019,\n13, 5703-5711). The fabricated fibers exhibit a remarkably uniform diameter of 180.2 μm, a\nhigh porosity of 96.7%, and a substantial tensile strength of 10.3 MPa. SEM imaging confirms\n8\nthat they are composed of a three-dimensional network of nanofibers (Supplementary Fig. 38b).\nThis thorough characterization validates the control sample as a representative benchmark for\nour comparative analysis.\nThe preparation method and detailed characterization data (Figure R4) for the Kevlar-ANF-\nAF control sample have been added to the revised Supplementary Information of\nSupplementary Fig. 39f:\nFigure R4. A table summarizing and comparing key spinning parameters and their\ncorresponding final fiber performance.\nQ7: There is a notable difference between the thermal conductivity of a single fiber (22.0\nmW·m-1·K-1) and the final knitted fabric (43.5 mW·m-1·K-1). While this is expected, a more\ndetailed discussion is needed. Could the authors please elaborate on why the knitted structure\nwas chosen and the factors influencing its thermal resistance?\nOur response:\nWe thank the reviewer for raising this important point about the discrepancy between single-\nfiber and fabric-level thermal conductivity.\nThe increase in thermal conductivity from a single fiber (22.0 mW·m-1·K-1) to the knitted fabric\n(43.5 mW·m-1·K-1) is an expected outcome rooted in the introduction of a new, macroscopic\nscale of heat transfer pathways.\nFirst, the key factors are the primary reason for the increased thermal conductivity in the\nfabric: The transition from a single fiber (22.0 mW·m-1·K-1) to a fabric (43.5 mW·m-1·K-1)\nintroduces macroscopic inter-yarn pores. The macroscopic pores (interstices) between the yarn\nloops in the knitted fabric are much larger than the mean free path of air (~70 nm) (Ref.: Adv.\nMater. 2024, 37, 2411856). This allows for natural convection to occur within the fabric\nstructure, which significantly increases heat transfer compared to the suppressed gas conduction\nwithin the aerogel fibers nanopores (Ref.: J. Text. Eng. Fash. Technol., 2017, 2, 401-409;\nCompos. Struct., 2019, 215, 278-288). While this increases heat transfer, these air channels are\nalso essential for the fabric's breathability, a key aspect of wearer comfort.\nCrucially, the solid-state conduction component remains fundamentally suppressed. The heat\n9\ntransfer through the solid yarn backbone is still governed by the intrinsic properties of the\naerogel fiber itself, where the nanostructured fibrillar network creates highly tortuous paths and\nimmense interfacial thermal resistance, effectively scattering phonons. This inherent, ultra-low\nsolid conductivity of the aerogel yarn is the foundational reason for the fabric's superior\nperformance compared to textiles made from conventional solid fibers.\nSecond, we chose the knitted structure to optimize overall thermal comfort. The knitted\nstructure provides indispensable benefits for both thermal performance and wearability (Ref.:\nNat. Commun., 2024, 15, 2622). The looped, point-contact nature of knitting minimizes the\nnumber and area of thermal bridges between yarns. These knitting fabrics, where extensive,\nhigh-pressure intersections create more direct pathways for solid heat transfer. Its three-\ndimensional, lofty architecture is exceptionally effective at trapping a thick, macroscopic layer\nof static air, which significantly contributes to the overall thermal resistance of the garment.\nFurthermore, the inherent coil structure of knitting imparts essential flexibility, stretchability,\nand durability, alleviating mechanical stress on the aerogel fibers and ensuring the textile\nrobustness for wearable applications.\nIn conclusion, the superior performance of our textile is a multi-scale achievement: the aerogel\nfiber itself provides a fundamentally low-conduction solid backbone, while the knitted\narchitecture is strategically employed to minimize thermal bridging, trap insulating air, and\nprovide the mechanical resilience necessary for a high-performance wearable garment.\nWe supplemented the corresponding descriptions in the revised manuscript on Lines 344-349,\nPage 17:\n“This value is higher than that of a single fiber, primarily due to convective heat transfer within\nthe fabric’s macroscopic pores47. Nevertheless, the knitted architecture was deliberately\nselected for its unique advantages in wearable thermal management. The interlooping structure\nprovides critical flexibility and resilience, while simultaneously trapping a substantial layer of\nstatic air to enhance the overall breathable and insulation performance of the garment48.”\nAdded references in the revised manuscript:\n1. Zhou, L.C., Sun, X.H., Chen, M.W., Zhu, Y.B. & Wu, H.A. Multiscale modeling and theoretical\nprediction for the thermal conductivity of porous plain-woven carbonized silica/phenolic\ncomposites. Compos. Struct. 215, 278-288 (2019).\n2. Singal, K. et al. Programming mechanics in knitted materials, stitch by stitch. Nat. Commun. 15,\n2622 (2024).\nComments: The manuscript entitled “Knittable, thermally insulating, and sustainable aerogel\nfibers enabled by ion-mediated hierarchical assembly” by Gang Xiao and co-workers presents\na well-designed ion-mediated hierarchical assembly strategy for producing heterocyclic\naramid aerogel fibers with both high mechanical strength and ultralow thermal conductivity.\nThe study is notable by comprehensive multiscale characterization and the effective integration of\nsimulations with experiments to elucidate the underlying mechanisms. While the approach\neffectively addresses the trade-off between mechanical robustness and thermal insulation in\naerogel fibers, several aspects require further improvement before the manuscript can be\nrecommended for publication:\nOur response:\nWe appreciate your positive evaluation of our manuscript and the valuable suggestion for\nperfecting this work. Please find the response and revisions for your detail comments as follows.\nQ1: The Introduction should be revised to provide a clearer comparative framework between\ntraditional aramid fibers and the proposed aerogel fibers, particularly in terms of performance\nand sustainability. This will help highlight the main advances: improved structural\ncontrollability and end-of-life recyclability.\nOur response:\nWe sincerely appreciate your constructive suggestion. We completely agree that establishing a\ndirect comparative framework against traditional aramid fibers will significantly strengthen the\nIntroduction and better highlight the impact of our work. Thus, we explicitly contrast aramid\naerogel fibers with conventional, dense aramid fibers, focusing on the two key advances you\npointed out:\nFirst, we have provided a detailed, quantitative comparison of thermal performance and its\nstructural origins. Conventional aramid fiber manufacturing processes, prioritizing mechanical\nperformance, yield highly crystalline and oriented molecular structures, often at the expense of\nother properties. This results in an extremely low porosity (typically < 0.004%) and a dense,\nsolid architecture (Ref.: Nat. Commun., 2023, 14, 3019). While this guarantees high strength\n(~ 30 GPa) and modulus (theoretical Young’s modulus > 120 GPa) (Ref.: Nat. Mater. 2022, 22,\n18-35), it also creates continuous pathways for phonon transport, resulting in a relatively high\nthermal conductivity of ~0.5 W·m-1·K-1 (Ref.: ACS Appl. Mater. Inter., 2025, 17, 62557-62568).\nIn stark contrast, the aerogel fiber strategy transforms this dense material into a three-\ndimensional network structure. The importance of this architecture synergistically suppresses\nheat transfer through multiple mechanisms: (i) phonon scattering and tortuous conduction paths\nwithin the solid nanofiber network, (ii) suppression of gas convection via nanoconfinement\n11\n(Knudsen effect), and (iii) reflection of thermal radiation by the multilayered structure (Ref.:\nScience 2019, 363, 6428, 723-727). This multi-physics heat-blocking effect is why aramid\naerogel fibers can achieve an ultralow thermal conductivity of <0.024 W·m-1·K-1 (Ref.: Nat.\nCommun. 2025, 16, 2357), an order of magnitude lower than their conventional counterparts.\nIn present work, we address the central challenge of precisely engineering pore architecture,\nincluding size, orientation, and hierarchical design, to achieve such a massive reduction in\nthermal conductivity while simultaneously enhancing mechanical strength for viable textile\nprocessing.\nSecond, we emphasized the significant recycling and sustainability challenges with derived\nthermal-isolating aerogel fibers. The revised Introduction provides a more detailed explanation\nof the difficulty in recycling conventional aramids. The robust hydrogen bonding networks and\nhigh crystallinity that impart exceptional strength to aramid fibers also render them chemically\ninert and extremely resistant to deconstruction at end-of-life, leading to a linear “use-and-\ndispose” lifecycle. In contrast, we offer a circular pathway through chemical dissolution and\nreuse strategy. Specifically, it has been demonstrated that a superbase-mediated chemical\nexfoliation method can effectively disrupt the strong intermolecular hydrogen bonds in waste\naramid fibers, liberating pristine nanofibers (Ref.: ACS Nano 2019, 13, 5703-5711). These\nnanofibers can then be redispersed to form a spinning dope, enabling the regeneration of high-\nperformance aerogel fibers. This process effectively closes the materials loop, transforming\nwaste into a valuable resource for a high-value production.\nIn response to your comment, we have added the corresponding descriptions in the revised\nmanuscript of the Introduction on Lines 59-70, Page 3:\n“The rigid polymers with conjugated backbones, such as aramids, intrinsically contain inter-\n(e.g., hydrogen-bonding, π-stacking) and intramolecular (e.g., C-C, C=C) interactions to\nguarantee the exceptional strength (~ 30 GPa) and high modulus (theoretical Young’s modulus >\ncrystalline packing compromises in moderate thermal insulation and creates significant end-of-\nlife challenges, as the robust interactions render conventional fibers notoriously difficult to\nrecycle. To address these dual challenges of performance and sustainability, a transformative\nstrategy involves deconstructing waste aramid fibers into their nanoscale building blocks,\naramid nanofibers (ANFs), and reassemble them into porous aerogel architectures. This\napproach not only enables a circular life cycle through material upcycling but also provides a\nversatile platform for unprecedented structural control. The resulting high-aspect-ratio ANFs,\nwith their rich surface chemistry, can be engineered into form an interconnected nanoporous\nnetwork for underpinning stress redistribution and enabling efficient axial stress transfer19-21”.\nWe believe this new framing more effectively underscores the novelty and importance of our\nfindings from the outset.\n1. Luo, J.J. et al. Fabricating strong and tough aramid fibers by small addition of carbon nanotubes.\nNat. Commun. 14, 3019 (2023).\n2. Lee, M. et al. Network of cyano-aramid nanofibres creates ultrastiff and water-rich hydrospongels.\nNat. Mater. 23, 414-423 (2024).\n3. Liao, W.H. et al. Low-Filler, High-Thermal-Conductivity Aramid Insulating Paper: Constructing\nEffective Thermal Conduction Networks via Boron Nitride/Aramid Composite Fibers. ACS Appl.\nMater. Interfaces 17, 62557-62568 (2025).\n4. Xu, X. et al. Double-negative-index ceramic aerogels for thermal superinsulation. Science 363,\n723-727 (2019).\nQ2: The stability of the fibers under operational conditions such as mechanical fatigue and\nhumid aging should be verified.\nOur response:\nWe appreciate your valuable comments. This is a crucial point regarding the practical durability\nof HANF-AFs. We have supplemented the structure evaluation after humid aging and the\nmechanical fatigue test to assess the stability of the fibers.\nFor mechanical fatigue test: we have systematically evaluated both the bending and tensile\nfatigue resistance of HANF-AFs as shown in Figure R5 (added as Supplementary Fig. 51) to\nverify its compelling mechanical durability of HANF-AFs.\n(i) Bending fatigue resistance: The HANF-AF yarn was subjected to 5,000 repeated 180°\nbending cycles (as demonstrated in Figure R5a, b). Post-cycling SEM analysis revealed only\nminimal surface deformation and the formation of minor micro-cracks, with the overall fiber\narchitecture maintaining its structural integrity (as depicted in Figure R5c). This performance\ndemonstrates remarkable flexibility and damage resistance, indicating suitability for the rigors\nof weaving, knitting, and daily wear.\n(ii) Tensile fatigue resistance: In parallel, cyclic uniaxial tensile fatigue tests were performed\non HANF-AFs to assess their mechanical fatigue. The single fibers derived from batch-prepared\nHANF-AFs yarns generally present a diameter of approximately 85 µm, a tensile strength of\n~83.1 MPa, a maximum load of ~0.45 N, and a fracture elongation of ~18%. To probe their\nfatigue resistance, cyclic tensile experiments were carried out at three distinct load amplitudes,\nrepresenting 22.2%, 44.4%, and 66.7% of the various load (0.1 N, 0.2 N, and 0.3 N), which\nresult in applied stress levels of 18.5 MPa, 36.4 MPa, and 54.7 MPa, respectively (Figure R5d).\nAs shown in Figure R5d, a distinct hysteresis loop was observed during the first cycle,\nsuggesting initial structural adaptation. Subsequent cycles rapidly stabilized, with loading-\nunloading curves exhibiting high reproducibility. At the lowest applied stress (18.5 MPa), the\n13\nstress-strain curves exhibited minimal hysteresis, indicating negligible energy dissipation and\nexcellent elastic recovery. Conversely, at the highest stress level of 54.7 MPa, significant\nhysteresis emerged, accompanied by a progressive increase in residual strain and a concomitant\nreduction in apparent elastic modulus with cycling. This behavior suggests cumulative damage\ndevelopment under elevated stress. Notably, even after 5,000 cycles, the fibers maintained\nstructural integrity without fracture, demonstrating highly stable elastic behavior. The\naccumulated residual strain remained negligible (0.8%, 1.0%, 1.7% respectively), confirming\nexceptional tensile fatigue resistance and excellent structural resilience. In conclusion, these\ncomplementary tests confirm that the HANF-AFs possess comprehensive mechanical durability,\nrendering them highly suitable for manufacturing robust and long-lasting textiles.\nWe have added the corresponding Mechanical fatigue resistance data of Figure R5 as\nSupplementary Fig. 51, and supplemented the corresponding descriptions in the revised\nmanuscript on Lines 281-284, Page 14:\n“The drafted AF mixture achieves a tensile strength of 111.2 MPa, representing a 271%\n2wt%H₂SO₄\nenhancement over its undrawn counterparts (30.4 MPa, Fig.4d and Supplementary Figs.48 and\n49, and Table1). Beyond these impressive static properties, the fibers exhibit excellent dynamic\nperformance critical for textile applications. They demonstrate outstanding fatigue resistance,\nrobustly withstanding 5,000 cycles of both severe 180° bending and high-stress tensile loading\nwith negligible degradation (Supplementary Fig. 51).”\nFigure R5. Mechanical fatigue resistance and durability of the HANF-AFs.\n(a) Photographs and corresponding (b) schematics illustrating the setup for cyclic bending tests,\n14\nwhere the HANF-AFs yarn was repeatedly bent from 0° to 180°. (c) SEM images of the fiber\nmicrostructure before (left) and after (right) 5000 bending cycles. The fiber shows slight\ndeformation. (d) Cyclic stress-strain curves from tensile tests. The fiber was subjected to 5,000\nloading-unloading cycles at various the various load levels of 0.1 N, 0.2 N, and 0.3 N,\nrespectively (the maximum tensile stress of 18.5 MPa, 36.4 MPa, and 54.7 MPa), showing\nstable mechanical behavior.\nFor humid aging test: we exposed the HANF-AFs to an accelerated aging environment of\n50%, 70%, 90% relative humidity (RH) for 24 hours. Optical photography confirmed negligible\ndimensional change in HANF-AF after exposure to 90% RH for 24 hours (Figure R6a,\nadded as Supplementary Fig. 66 in Supporting Information). Post-aging characterization revealed that\nthe fiber’s hierarchical porous microstructure remained intact, as confirmed by SEM imaging\nin Figure R6b. These observations collectively attest to exceptional structural stability under\nhigh-humidity conditions.\nWe have added the corresponding humid aging test data of Figure R6 as Supplementary Fig.\n69, and supplemented the corresponding descriptions in the revised manuscript on Lines 372-\n375, Page 18:\n“Furthermore, after encapsulation of HANF-AF within thermoplastic polyurethane (TPU),\nstable water repellency and thermal insulation were achieved (Supplementary Figs. 69, 71 and\n72), establishing a foundation for next-generation machine-washable thermal insulating\ntextiles.”\nFigure R6. Structural stability of the HANF-AFs under varying relative humidity\nconditions.\n(a) Optical microscopy images of HANF-AF fibers, following 24 hours of exposure to 90%\nmorphology of the HANF-AFs after being equilibrated for 24 hours at different relative\nhumidity (RH) levels (e.g., from left to right: 50%, 70%, 90% RH). The images reveal that the\nfiber maintains its porous architecture and structural integrity even at high humidity,\ndemonstrating its excellent humidity stability.\nQ3: The comparative analysis should be expanded to include common high-performance\ninsulating fibers such as aramid and PI. For a fair evaluation, the thermal and mechanical\nproperties should be compared at the same areal density or thickness.\nOur response:\nThank you for the valuable suggestion to enhance the comparative analysis. We have addressed\nyour points as follows:\nFirst, we have incorporated data for common high-performance insulating fibers (Polyimide\n(PI) and Aramid). The added knitted fabric utilizing commercial PI and aramid yarns have been\nprepared. Their thermal conductivity has been also included in the comparative analysis,\npresented in Figure R7 (supplemented as Supplementary Fig. 66 in Supporting Information),\nbroadening the scope beyond conventional textiles.\nSecond, during the knitting process, while we sought to maintain consistent yarn diameters\nacross all materials (PI, aramid, silk, cotton, polyester), inherent variations in yarn properties\n(modulus, stiffness) resulted in differences in the resulting fabric areal density and thickness.\nTo provide a direct and equitable comparison of the intrinsic thermal insulation performance\nacross materials, and structural differences, we have normalized the data by calculating the\nthermal conductance (λ/d) based on the thickness of each fabric. This value (in W·m-2·K-1)\nrepresents the rate of heat transfer per unit area per unit temperature difference, effectively\neliminating the influence of fabric structure (such as thickness). The updated data clearly\ndemonstrate that HANF-AF fabric exhibits a thermal conductance of 53.0 W·m-2·K-1. This\nvalue is approximately 17.6% lower than that of the aramid fabric (64.3 W·m-2·K-1) and 29.4%\nlower than that of the PI fabric (75.1 W·m-2·K-1). The normalized results are now presented in\nthe Table R1 (added as Supplementary Table 2 in Supporting Information).\nHowever, compared to assessing the thermal resistance of fabrics, thermal conductivity is a\nmore intuitive and widely accepted metric for researchers, facilitating horizontal comparison.\nTherefore, we only present the normalized comparison results (W·m-2·K-1) in the revised\nSupplementary Table 2. We have added the test results for the thermal conductivity of the PI\nfabric in the revised manuscript on Line 344, Page 17.\n“The float-plated HANF-AF fabric with a minimal thickness of 0.82 mm, exhibits a thermal\nconductivity of 43.5 ± 1.2 mW·m-1·K-1, which is significantly inferior to polyimide (75.1\n16\nmW·m-1·K-1), aramid (64.3 mW·m-1·K-1), silk (72.7 mW·m-1·K-1), cotton (66.3 mW·m-1·K-1),\nand polyester (93.7 mW·m-1·K-1) (Supplementary Figs.64-66 and Table2 and Movie3).”\nFigure R7. Fabric structure and thermal conductivity (λ).\n(a) Photographs of HANF-AF, polyimide, aramid, silk, cotton, and polyester fabrics structural,\nrespectively. (b) The thermal conductivity (λ) of fabrics was measured with a Hot disk thermal\nanalyzer.\nTable R1. Knitting parameters for the HANF-AF fabric and control samples.\nThermal\nAreal density Fabric λ/ thickness\nKnitted fabric conductivity (λ)\n(g cm-2) thickness (mm) (W·m-2·K-1)\n(mW·m-1·K-1)\nHANF-AF 0.037 0.82 43.5 53.0\nPolyimide 0.071 0.79 59.3 75.1\nAramid 0.059 0.83 64.3 77.5\nSilk 0.065 0.82 72.7 88.7\nCotton 0.061 0.91 66.3 72.9\nPolyester 0.060 0.84 93.7 111.5\nQ4: The connection between the CG-MD simulations and the experimental data should be\nstrengthened. We recommend directly relating the simulation results to measurements such as\nzeta potential and FT-IR spectra to provide a clearer basis for the proposed hierarchical\nassembly mechanism.\nOur response:\nWe appreciate the reviewer’s insightful suggestion. We agree completely that strengthening the\nconnection between our CG-MD simulations and the array of experimental data is crucial for\nproviding a robust and clear basis for our proposed hierarchical assembly mechanism, as\ndescribed as follows. To address the reviewer’s concern, we have substantially revised to build\n17\na more explicit, quantitative, and logical bridge between the simulations and our key\nexperimental findings.\nFirst, a direct quantitative correlation has been established between the charge\nparameters in the CG-MD simulation and the experimentally measured zeta potential.\nThe simulation models the protonation process by systematically reducing the negative charge\non each nanofiber bead. This parameter directly corresponds to the experimentally measured\nsurface charge. For instance, the simulation shows that reducing the bead charge from 71% to\n23% to 0% mirrors the experimental decrease in zeta potential from -46.1 mV (in the initial\nbasic state) to -14.3 mV (the critical point for aggregation) to -1.1 mV (neutral pH) upon acid\ntitration (Fig. 3c). The charge attenuation quantified in simulations aligns with the weakening\nof electrostatic repulsions fitted in HANF colloidal systems. This quantitative alignment\nvalidates our simulation model and confirms that the experimentally observed aggregation is\ntriggered by the attenuation of Coulombic repulsion, which the simulation accurately captures.\nSecond, CG-MD simulations provide a mechanistic explanation for the spectroscopic (FT-\nIR and UV-vis) results. Simulation analysis exhibits an increase in stable intermolecular\ninteractions (mainly referring to H-bond pairs), defined by Radius of gyration values decrease\nfrom 6.95 nm to 6.56 nm, (lifetime < 2 ns) under acidic conditions (Supplementary Figs. 25-\n27). This mechanistic prediction is experimentally confirmed by FT-IR, such as the C=O bond\nshifts from 1657 cm-1 to 1664 cm-1 as shown in Supplementary Fig. 18, while the imidazole N-\nH stretching peak intensity rises >50%. These structural rearrangements drive the electronic\nstate transition observed in UV-vis spectra (Fig. 3d and Supplementary Fig. 19), where the\nπ→π* absorption peak from 420 nm to 360 nm. This spectral shift indicates enhanced π-\nconjugation resulting from molecular planarization mediated by hydrogen bonding.\nThird, the multi-stage assembly process revealed by CG-MD simulations provides a direct\nlink to the macroscopic phase separation and rheological behavior. The simulated nanofiber\nassembly process exhibits acid-induced entanglement through two stages: (i) rapid nucleation\n(< 2 ns) via charge screening and (ii) oriented bundling (2-50 ns) governed by H-bond\nalignment. This simulated process provides a microscopic explanation for the experimentally\ndetermined ternary phase diagram (Fig. 3e and Supplementary Fig. 22). The simulation shows\nthat reduced electrostatic barriers (i.e., lower pH) lower the energy cost for this aggregation,\nwhich directly explains why the phase separation boundary shifts, reducing the required non-\nsolvent (water) concentration for a 2 wt% HANF dispersion from 30 vol% (at neutral pH) to\n10 vol% (in 2 wt% acid). Finally, the formation of a percolating network in the simulation\ndirectly accounts for the macroscopic gelation observed in rheology (Fig. 3f and Supplementary\nFig. 23). The simulation shows that at a critical degree of charge reduction (corresponding to\nthe experimental gel point), the aggregated clusters connect to span the entire system. This is\nperfectly mirrored by the experiment, where the zero-shear viscosity dramatically increases by\n18\n8.4-fold at the critical acid concentration of 0.5 wt%, signaling the formation of a load-bearing,\nsystem-spanning gel network.\nIn summary, these revisions now present a cohesive, multi-scale narrative where the CG-MD\nsimulation acts as a connecting bridge, providing a direct, quantitative, and mechanistic link\nbetween molecular-level interactions (FT-IR, UV-vis), surface phenomena (Zeta potential),\nthermodynamics (phase diagram), and macroscopic properties (rheology).\nWe have therefore added the following content to the discussion in the revised manuscript on\nLines 217-229, Pages 10-11:\n“In simulations modeling the experimental protonation assembly, we progressively reduced the\nnegative charge on nanofiber beads, directly mimicking the attenuation of electrostatic\nrepulsion (quantified by Zeta potential as high, moderate, and low, Fig. 3g). These simulations\nprovide compelling visual confirmation of gelation (Fig. 3g and Supplementary Figs. 24-27),\nrevealing that reduced Coulombic repulsion triggers nanofibers coalescence into denser\naggregates (driven by short-range attractions) while expanding inter-aggregate voids. This\nsimulated aggregation provides a direct mesoscopic snapshot that connects the molecular-level\nH-bond reconstruction (FT-IR) and electronic transitions (UV-vis) to the macroscopic\nthermodynamic changes (phase diagram, Fig. 3d and 3e) and gelation (rheology, Fig. 3f).\nCollectively, spectroscopy, zeta potential, phase mapping, rheology, and CG-MD simulations\nform a cohesive, multi-scale framework. This demonstrates that modulating electrostatic\nbarriers through protonation kinetics deterministically controls coagulation dynamics and\nhierarchical pore architecture, enabling precise microstructural engineering of HANF-AFs.”\nQ5: The analysis of the thermal conduction mechanisms, although noting effects such as\nphonon scattering, would benefit from a more systematic theoretical treatment. Quantifying the\ncontribution of these effects or comparing the measured conductivity with established models\nwould provide a clearer and more rigorous validation of the proposed mechanisms.\nOur response:\nWe thank the reviewer for such a great suggestion. We agree that a deeper theoretical treatment\nis essential for validating our proposed structure-property relationships.\nWe have framed our analysis within an established theoretical model. As described in the\nliterature (Ref.: Adv. Mater. 2018, 30, 1706807; Adv. Mater. 2019, 31, 1801001), the total\neffective thermal conductivity (λ ) of HANF-AF is determined by the sum of four critical\nHANF-AF\ncomponents: solid conduction (λ ), gas conduction (λ ), convection (λ ), and thermal\nsolid gas conv\nradiation (λ ). While accurately quantifying the contribution of each component in a complex\nrad\nhierarchical system is a formidable challenge, we have conducted new experiments and a\ndetailed analysis to demonstrate that the hierarchical porous architecture synergistically\n19\nsuppresses each of these heat transfer pathways.\nFor λ and λ : The hierarchical architecture is composed of a nano-porous core and a\ngas solid\nmacro-porous cellular shell, with the entire solid matrix built from an interconnected network\nof ultrafine nanofibers featuring sub-50 nm pores (Fig.4c, and Supplementary Figs. 38, and 41-\n42). This hierarchical design provides a dual-pronged suppression mechanism. The sub-50 nm\npores create strong nanoconfinement, leading to a significant Knudsen effect that drastically\nreduces gas-phase conduction (λ ). Simultaneously, the solid backbone is a three-dimensional\ngas\nnetwork of 3.4 nm ultrafine nanofibers. The nanofibrillar network itself minimizes solid\nconduction (λ ) through intense phonon scattering at the countless nanofiber interfaces and\nsolid\nthrough highly tortuous heat conduction pathways.\nFor λ : Both the of macro-porous cellular shell and sub-50 nm pores play a crucial role in\nconv\nmanaging convection. It compartmentalizes air into semi-enclosed cells, which restricts the\nformation of large-scale convective loops that are typically present in textile structures. This\nstructural feature helps to minimize the contribution of λ .\nconv\nFor λ : To specifically investigate radiative heat transfer, we performed new experiments\nrad\npresented in Figure R9 (added as Supplementary Fig.60 in the revised Supporting Information).\nAs shown in Figure R9a, the transmittance in the IR region is typically associated with the\ninherent molecular structure of aramid molecular bonds (Ref.: Nat. Commun., 2025, 16, 2009).\nHowever, our results clearly demonstrate that both establishing a hierarchical structure and\nincreasing the material thickness independently and significantly enhance the suppression of\nIR transmission. This indicates that both of the orientation (Supplementary Fig. 49; Ref.:\nScience, 382, 2023, 1379-1383) and the hierarchical architecture (Fig. 4c and Supplementary\nFig. 42; Ref.: Sci. Adv. 2019, 5, eaat9480; Ref.: Nat. Commun., 2023, 14, 6129) contributes\nare strongly related to infrared reflection. Furthermore, we tested the HANF-AF fabric\ninsulation performance on a hot substrate with and without a low-emissivity aluminum foil to\nisolate the effect of radiation from the heat source. The nearly identical temperature differences\n(ΔT) observed (Figure R9b) provide compelling evidence that our fabric acts as an effective\nintrinsic radiation barrier, capable of blocking thermal radiation.\nIn summary, we concluded based on a comprehensive, synergistic mechanism. The ultralow\nthermal conductivity is not the result of a single dominant mechanism but of a hierarchical co-\nsuppression strategy: the sub-50 nm pores inhibit λ , the nanofiber network inhibit λ ,\nthe\ngas solid\ncellular shell manages λ , and the entire hierarchical architecture synergistically blocks λ\nconv rad\n(Figure R8). This integrated approach to heat management is the core advantage of our material\ndesign.\nWe modified Figure R8 as Fig. 4g, and the figure now emphasizes the crucial role of our\nHANF-AF’s functional architecture in reducing heat transfer Line 234, Page 12.\nSimultaneously, we have added new data regarding thermal radiation to Figure R9 as\nthe hierarchically porous HANF-AFs in the revised manuscript on Lines 302-310, Pages 14-\n15：\n“Concurrently, the macro-porous cellular shell compartmentalizes air into semi-enclosed cells,\nthereby suppressing large-scale convective loops. Furthermore, solid phase thermal conduction\nis minimized through interfacial phonon scattering within the ultrafine (3.4 nm) nanofibrillar\nnetwork and the elongation of heat transfer pathways. The hierarchical architecture also\nfunctions as an intrinsic and efficient radiation barrier, effectively attenuating thermal radiation\n(Supplementary Fig. 60)3, 44-46. Therefore, this exceptional insulating performance arises not\nfrom a single mechanism but from the synergistic suppression of all four heat transfer modes—\ngas conduction, solid conduction, convection, and radiation—enabled by the hierarchical\ndesign. This integrated approach achieves a remarkably low thermal conductivity of 22.0\nmW·m-1·K-1 with a porosity of 89.1%.”\nFigure R8. Schematic illustration of the thermal conductivity of porous fibers with hierarchical\npore structures and isotropic three-dimensional network structures.\nFigure R9. Radiative heat transfer management of the HANF aerogel materials.\n21\n(a) Infrared transmittance spectra of various aerogel sample films: an isotropic film (~125 µm),\na hierarchical fiber (~100 µm), and a thick hierarchical film (~340 µm). The low IR\ntransmittance is attributed to the inherent vibrational absorption of the aramid molecules and\nenhanced scattering by the hierarchical pore structure. Both establishing a hierarchical structure\nand increasing the thickness of aerogel materials independently contribute to suppressing\ninfrared transmission. (b) Characterization of thermal insulation performance (ΔT) of HANF-\nAF fabric on a standard hot substrate (with thermal radiation) versus a hot substrate covered\nwith low-emissivity aluminum foil (to eliminate thermal radiation). The nearly identical\ntemperature differences (ΔT) observed under both conditions provide compelling evidence that\nthe fabric possesses ability to block thermal radiation.\nAdded references in the revised manuscript:\n1. Cui, Y., Gong, H.X., Wang, Y.J., Li, D.W. & Bai, H. A Thermally Insulating Textile Inspired by\nPolar Bear Hair. Adv. Mater. 30 (2018).\n2. Leroy, A. et al. High-performance subambient radiative cooling enabled by optically selective and\nthermally insulating polyethylene aerogel. Sci. Adv. 5, eaat9480 (2019).\n3. Xiong, L.H. et al. Thin lamellar films with enhanced mechanical properties for durable radiative\ncooling. Nat. Commun. 14, 6129 (2023).\nQ6: Given cost considerations, aramid aerogel fibers are mainly suited for high-end\napplications such as aerospace and specialized firefighting protection. These environments\noften involve dynamic, non-isothermal conditions. It would therefore be useful to include data\non the fibers’ thermal insulation performance under dynamic temperature cycling.\nOur response:\nWe appreciate the reviewer’s insightful comment regarding the high-end applicability and\nperformance requirements for HANF-AF. To directly address this critical point on operational\nresilience, we have conducted a systematic evaluation of the thermomechanical durability under\ndynamic conditions.\nFirst, comprehensive evaluation confirms the intrinsic thermomechanical robustness of\nHANF-AFs across an extreme operational range (-196 ℃ to 500 ℃). As evidenced in Figure\nR10a, the HANF-AFs maintains its structural integrity and mechanical flexibility after being\nimmersed in liquid nitrogen (-196 °C). Additionally, thermogravimetric analysis (TGA) in\nFigure R10b demonstrates exceptional thermal stability, with negligible mass loss sustained\nup to the onset decomposition temperature of 500 °C, confirming its robustness across a\nrigorous temperature range.\nSecond, the thermal resilience of the HANF-AFs insulation capability under dynamic thermal\ncycling was also rigorously validated. The HANF-AFs were subjected to repeated thermal\n22\nshock cycles, alternating between cryogenic temperatures (-196 °C, liquid nitrogen) and high\ntemperatures (200 °C, hot substrate). As shown by the consistent temperature profiles in the\nthermal images taken before and after cycling (Figure R10c, d), the HANF-AFs demonstrated\nexcellent thermal insulation stability without discernible degradation. This result confirms the\nstructural durability and reliable performance even after repeated exposing to extreme\noscillating temperature.\nIn conclusion, Figure R10 (added as Supplementary Fig.70 in the revised Supporting\nInformation) provides empirical validation of the HANF-AF exceptional thermomechanical\nresilience and reliable insulating performance under demanding dynamic thermal conditions.\nThese findings substantiate its suitability for specialized applications such as aerospace systems\nand firefighting protective gear.\nThus, we revised the corresponding discussion in the revised manuscript on Lines 369-372,\nPage 18:\n“The HANF-AF fabric exhibits exceptional thermal durability, maintaining over 97% of its\noriginal insulating capability after undergoing repeated thermal cycling between 100 °C and -\n196 °C (Supplementary Fig. 70). This resilience highlights its reliability for applications in\nsubject to extreme and dynamic temperature fluctuations.”\nFigure R10. Performance stability of the HANF aerogel fiber in extreme thermal\nenvironments.\n23\n(a) A sequence of photographs showing a HANF aerogel yarn being immersed in liquid nitrogen\n(-196 °C), bent, and subsequently recovering its original shape upon thawing. This\ndemonstrates the fiber’s remarkable cryogenic flexibility and structural integrity. (b)\nThermogravimetric analysis (TGA) curve of the aerogel fiber under a N₂ atmosphere. The data\nindicate excellent thermal stability with a decomposition onset temperature above 500 °C. (c)\nInfrared (IR) thermal images assessing the insulation performance both before (left) and after\n(right) subjecting the fiber mat to extreme temperature cycling (between -196 °C and 200 °C).\n(d) The nearly identical temperature profiles (ΔT) confirm the robust and stable thermal\ninsulation capability of the material.\nQ7: It is noted that scaling up the wet-spinning process requires substantial use of the key\nsolvent DMSO, despite the manuscript highlighting process recyclability. The authors should\nclarify how DMSO is handled during post-processing and whether its high consumption affects\nthe overall sustainability and cost-effectiveness of the proposed strategy.\nOur response:\nThank you for raising this important concern regarding practical and economic viability. The\nefficient recycling of DMSO is indeed a crucial factor for the scalability and cost-effectiveness\nof our proposed strategy. We have addressed this consideration by revising the Supplementary\nInformation (Figure R11, added as Supplementary Fig. 13b) to clarify the feasibility and\nsignificance of implementing a DMSO recovery process.\nFirst, the recovery of DMSO from the aqueous coagulation and washing baths is highly feasible,\nsupported by established industrial techniques. As illustrated in Figure R11, standard industrial\nseparation techniques, notably vacuum distillation, can be effectively employed. This process\nleverages the significant boiling point difference between DMSO (189 °C) and water (100 °C),\nenabling efficient and energy-conscious separation. This approach is not merely theoretical but\nrepresents a mature and well-documented technology, as evidenced in relevant literature (Ref:\nWater Res. 2021, 197, 117103), confirming its practical implementation in various industrial\nscenarios.\ndistillation and separation of DMSO from the coagulation bath mixture, enabling a closed-loop\nrecycling of the DMSO solvent for subsequent production batches.\nSecond, we have presented a preliminary cost-benefit analysis based on real-world industrial\ndata (Link: https://max.book118.com/html/2025/0119/5030010301012034.shtm). A detailed\ncalculation is now provided:\nPrice：cost of new DMSO: ¥20,000/ton; cost of recovery (operation + utilities + labor): ¥800/ton.\nScenario: Production of 1 ton of HANF-AFs (Spinning dope HANF content 2wt%, requires 50\ntons of DMSO).\nCost without recycling: 50 tons × ¥20,000/ton = ¥1,000,000\nCost with recycling: ¥40,000 + ¥200,000 = ¥240,000\nCost with recycling (80% rate): Recovery operation cost: 50 tons × ¥800/ton = ¥40,000\nCost of replenishing lost DMSO: 50 tons × 20% × ¥20,000/ton = ¥200,000 (DMSO recovery\nrate: 80%).\nCost reduction: ¥1,000,000 - ¥240,000 = ¥760,000\nCost reduction percentage: (¥1,000,000 - ¥240,000) / ¥1,000,000 × 100% = 76%\nBased on the market price of new DMSO (¥20,000/ton) and the operational cost of industrial-\nscale recovery (¥800/ton, including utilities and labor), we analyzed the economic impact of\nimplementing a recycling loop. This analysis demonstrates that implementing solvent recycling\ncan reduce the associated costs by a dramatic ~76%. This substantial saving is critical for\nensuring the economic feasibility of large-scale production.\nWe have updated the Supplementary Information to reflect these considerations to highlight the\nimportance of solvent recycling within closed-loop paradigm. We have supplemented an extra\ndiscussion at in the revised Supplementary Information (Supplementary Text 1) on Page 7,\nLines 195-201:\n“Crucially, for scaled-up production, the DMSO-laden aqueous effluents from the coagulation\nand washing stages were collected for recycling. The combined DMSO/water streams were\nthen purified via vacuum distillation, a common industrial process to recover DMSO, allowing\n25\nfor its reuse in the preparation of subsequent spinning dopes. This recycling protocol is critical\nfor ensuring the economic feasibility and environmental sustainability of the process.”\nQ8: For practical applications, the wash durability of the fabric should be addressed. It would\nalso be useful to report whether the performance of the aerogel fibers has been tested under\nhigh-humidity conditions, along with data on microstructural changes and thermal conductivity.\nOur response:\nThanks for your insightful question regarding the practical wash durability of our fabric. This\nis indeed a critical aspect for practical wearable applications.\nWe acknowledge that humid instability is an inherent challenge for most aerogel-based\nmaterials, including our HANF-AFs. The high specific surface area and porous nature of the\naerogel fibers make them susceptible to wetting. During the drying of a wetted fiber under\nambient conditions, the evaporation of liquid from the nanopores generates immense capillary\nforces, leading to irreversible pore collapse and structural shrinkage. As a result, an HANF-AF,\ndespite its high initial mechanical strength, suffers catastrophic structural degradation upon\nwashing, which would severely compromise its thermal insulation performance (Figure R12).\nTo overcome this fundamental challenge, and inspired by recent successful strategies in the\nfield (Ref.: Science 2023, 382, 1379-1383; Nature Commun. 2025, 16, 2357), we have\ndeveloped and validated a thermoplastic polyurethane (TPU) coating approach to impart water\nresistance and washability to our HANF-AFs.\nFirst, we successfully rendered the HANF-AFs hydrophobic via a conformal TPU coating. As\nshown in the cross-sectional SEM images (Figure R11ab), a uniform and dense TPU layer,\napproximately 2.5 µm thick, was applied to the fiber surface. This coating transformed the\noriginally hydrophilic fiber into a hydrophobic one, increasing the water contact angle to 111.2°\n(Figure R11cd).\nSecond, we confirmed that the TPU coating provides excellent wash durability and maintains\nthermal insulation performance. Visual inspection shows that the uncoated yarn suffers\nsignificant structural collapse after washing and drying, while the TPU-coated yarn maintains\nits structural integrity (Figure R12ab).\nThe washing process was simulated, and the performance of three samples was compared: (i)\noriginal uncoated fiber, (ii) uncoated fiber after washing, and (iii) TPU-coated fiber after\nwashing (Figure R12c-e). Most critically, thermal insulation tests demonstrate that the\nuncoated fiber's performance plummets after washing (the temperature difference, ΔT, drops\nfrom 10.6 °C to 4.8 °C). In stark contrast, the TPU-coated fiber retains the vast majority of its\ninsulation capability after washing (ΔT is 9.8 °C, retaining 92.5% of the original performance).\nIn conclusion, these results demonstrate that a simple TPU coating is a highly effective strategy\n26\nto impart hydrophobicity and wash durability to our HANF-AFs, protecting their nanoporous\nstructure and ensuring their excellent thermal insulation performance is maintained even after\nwashing.\nIn response to the reviewer’s comment, we have added the corresponding data of Figure R11,\nFigure R12 as Supplementary Fig. 71, Supplementary Fig. 72, and supplemented the\ncorresponding descriptions in the revised manuscript on Lines 372-375, Page 18:\n“Furthermore, after encapsulation of HANF-AF within thermoplastic polyurethane (TPU),\nstable water repellency and thermal insulation were achieved (Supplementary Figs. 69, 71 and\n72), establishing a foundation for next-generation machine-washable thermal insulating\ntextiles.”\nFigure R11. Surface wettability changes upon TPU coating of HANF-AFs yarn.\n(a) Cross-sectional SEM image of an initial HANF-AF, revealing a skin layer approximately\n0.5 µm thick. (b) Cross-sectional SEM image of a HANF-AF after coating with thermoplastic\npolyurethane (TPU). The TPU layer forms a denser, approximately 2.5 µm thick coating on the\nfiber surface. Contact angle images demonstrating the change in surface wettability of HANF-\nAF yarns before (c) and after (d) TPU coating. The initially hydrophilic HANF aerogel yarn\nbecomes hydrophobic after TPU modification, exhibiting a contact angle of 111.2°.\nTPU-coated HANF aerogel yarns.\nPhotographs showing the visual appearance of initial hydrophilic HANF-AF yarn (a) and TPU-\ncoated hydrophobic HANF-AF yarn (b) at three stages: as-prepared (original state), after\nwashing, and after atmospheric-drying. The images highlight the structural integrity of the\nTPU-coated yarn after water washing. Comparative analysis of the steady-state temperature\ndifference (ΔT) between the fiber mat (single-layer) and the hot plate, for different conditions:\n(c) initial HANF-AF yarn before washing, (d) HANF-AF yarn after water washing, and (e)\nTPU-coated HANF-AF yarn after washing. The measured ΔT values are 10.6 °C, 4.8 °C, and\n9.8 °C, respectively, confirming the crucial role of TPU coating in preventing the collapse of\nfiber pores and maintaining insulation performance after post-washing.\nZhang et al. report the fabrication of aerogel fibers derived from heterocyclic aramid nanofibers\nthrough an ion-mediated hierarchical assembly strategy. The resulting fibers exhibit a\ndual-scale porous architecture, combining a nanoporous core with a macroporous cellular shell,\nwhich enables the simultaneous achievement of exceptional tensile strength and ultralow\nthermal conductivity. Notably, the authors demonstrate a scalable fabrication route, including\nautomated knitting, highlighting strong application potential for thermal-insulating textiles. The\nexperiments are well-designed, supported by extensive characterization. I recommend the\npotential acceptance after minor revision.\nOur response:\nWe appreciate your positive evaluation of our manuscript and the valuable suggestion for\nperfecting this work.\nQ1: The authors should clarify the appropriateness of using the term “aerogel fibers.” The\nconcept of “aerogel” is often loosely or inconsistently used in the literature. Although the\nIUPAC definition implies microporous structures with pore sizes below 2 nm, even classical\nsilica aerogels typically exhibit pores of 10–50 nm (https://doi.org/10.1002/adma.202001839).\nIn this work, the pore sizes of the fibers are clearly larger than these commonly accepted ranges.\nThe authors should therefore explain why the material is categorized as an aerogel rather than\na foam or another type of porous fiber, and justify the terminology based on structural features,\nfunctional behavior, or prevailing conventions in aerogel research.\nOur response:\nWe thank the reviewer for this insightful question. We agree that the term “aerogel” is often\nused broadly, and providing a clear justification for its use in our work is important.\nFirst, our categorization of the HANF-AFs as an “aerogel fiber” is based on the modern, widely\naccepted definition of an aerogel (Ref. Adv. Mater. 2024, 2411856; Adv. Mater. 2021, 33,\n2005569), which emphasizes not only pore size but also a combination of key characteristics:\n(1) a three-dimensional network built from nanoscale building blocks, (2) high porosity and\nlow density, and (3) fabrication via a sol-gel process followed by a drying method that preserves\nthe porous network. Our HANF-AFs comprehensively meet these criteria.\nSecond, as the reviewer correctly noted, HANF-AFs exhibit a hierarchical architecture with\nmacroscopic pores. However, we wish to emphasize that the solid matrix of the fiber, including\nthe walls of these macroscopic cells and the entire core region, is fundamentally an\ninterconnected porous network material. This is directly substantiated by multiple lines of\nevidence:\n(i) Direct visualization of the porous architecture: High-magnification SEM of the fiber\n29\ncross-section (Fig. 4c) and cryo-FIB-SEM images along the fiber axis (Supplementary Fig. 42)\nboth clearly reveal a nanoporous core and a macro-porous cellular shell, which encloses\ninterconnected nanofiber spacing with sub-50 nm pores.\n(ii) Quantitative porosimetry data: Nitrogen adsorption-desorption (BET) analysis\n(Supplementary Fig. 38c) quantitatively confirms a high specific surface area and a significant\nvolume of pores within this sub-50 nm regime.\nIn conclusion, because our fibers are derived from a sol-gel process and consist of a continuous,\nnanoporous solid network, the term “aerogel fiber” is appropriate and consistent with prevailing\nconventions in the field.\nTo enhance clarity for the readers, we have revised the manuscript to more explicitly describe\nthis hierarchical structure. We have further added the new description in the revised the\nmanuscript on Page 13, Line 269-271:\n“This architecture contains gradient macropores (0.5-5 μm) within the shell layer and a fine\nnanoporous structure (3-50 nm) that constitutes the solid matrix of both the macropore walls\nand the core layer, as confirmed by mercury intrusion porosimetry (Supplementary Figs. 38,\n40-43).”\nQ2: The manuscript suggests a strong mechanical-thermal contradiction in aerogel fibers;\nhowever, the achievable performance range in related systems should be accurately reflected.\nFor example, in the cellulose-based aerogel fiber, tensile strengths as high as 71.83 MPa\ncoupled with thermal conductivities as low as 0.023 W m-1 K-1 have been reported\n(https://doi.org/10.1021/acs.nanolett.1c03943). The authors are encouraged to incorporate\nsuch representative data into the Introduction and adjust the comparative analysis in Figure 1c\naccordingly, ensuring a fair and comprehensive contextualization of the performance\nlandscape.\nOur response:\nWe thank the reviewer for bringing this important reference. To ensure a fair and comprehensive\ncontextualization of the performance landscape, we have updated our manuscript. The main\nrevisions are as follows:\nFirst, the performance of the high-performance cellulose-based aerogel fiber (tensile strength\nof 71.83 MPa) (Ref. Nano Lett. 2022, 22, 3516-3524) has been incorporated into the Ashby\ndiagrams in Figure R13 (added as Figure 1c).\nSecond, the discussion in the Introduction has been revised to acknowledge the significant\nprogress made in mitigating the mechanical-thermal trade-off in other material systems. We\nhave made corresponding modifications and references in the description of the Introduction\non Line 51, Page 3:\n“Despite extensive efforts dedicated to enhancing fiber strength from tens of kilopascals (kPa)\nto approximately 70 MPa8-13 (add the Ref.: Nano Lett. 2022, 22, 3516-3524), this is sufficient\nonly for manual weaving and insufficient to meet the demands of complex textile engineering.”\nAdded references in the revised manuscript:\n1. Li, Q.H. et al. Tough, Highly Oriented, Super Thermal Insulating Regenerated All-Cellulose\nSponge-Aerogel Fibers Integrating a Graded Aligned Nanostructure. Nano Lett. 22, 3516-3524\n(2022).\nQ3: The Kevlar-ANF images in Figure 2d appear similar to those published in previous studies.\nIf these images are reproduced, adapted, or modified from earlier literature, the original\nsources must be explicitly cited either in the figure caption or in the main text to ensure proper\nattribution.\nOur response:\nWe thank the reviewer for ensuring proper academic attribution. The width for Kevlar-ANFs\nof Kevlar-ANFs in Figure 2d was intended as a representative example for size comparison. To\nensure proper credit, we have now added an explicit citation to the original source in the figure\ncaption. A citation has been added in the revised manuscript on Line 143, Page 7:\n“(d) Frequency distribution of the width for individual HANFs and Kevlar-ANFs. The width\nfor Kevlar-ANFs is representative of found in the literature (Nat. Mater. 23, 414-423 (2024))37.”\nAdded references in the revised manuscript:\n1. Lee, M. et al. Network of cyano-aramid nanofibres creates ultrastiff and water-rich hydrospongels.\nNat. Mater. 23, 414-423 (2024).\nparticularly those related to the acquisition of UV–vis spectra, zeta-potential measurements,\nand the AFM characterization of HANFs. Providing these details is essential for ensuring\nreproducibility and enabling readers to accurately assess the methodology.\nOur response:\nWe thank the reviewer for this suggestion. The “Characterization and measurement” section in\nthe Methods has been updated with more detailed descriptions for the experimental procedures\nin the revised manuscript on Lines 419-426, Page 20:\n(i) UV-vis absorption spectra: “...were recorded on a UV-VIS-NIR spectrometer... For titration\nexperiments, a 0.125 wt% HANF dispersion was used, and the acidic titrant was pre-diluted in\nDMSO to prevent rapid, localized aggregation.”\n(ii) Zeta potential: “...was measured using a Zetasizer... The measurements were performed on\nHANF dispersions diluted to 1.0 mg/mL in a DMSO solution to ensure accurate readings.”\n(iii) Atomic force microscopy (AFM): “...was measured by atomic force microscopy... Samples\nfor AFM were prepared by depositing a 5 μL droplet of an ultra-dilute HANF suspension\n(0.00005 wt% in ethanol) onto a freshly cleaved silicon wafer (1×1 cm), followed by air drying.”\nQ5: The manuscript introduces three programmable wet-spinning strategies aimed at tailoring\nthe hierarchical pore structure of the aerogel fibers. However, direct experimental evidence\ndemonstrating the structural impact of each strategy is limited. The authors are encouraged to\ninclude comparative SEM images and corresponding analysis to clearly illustrate how each\nprocess parameter modifies the final pore morphology.\nOur response:\nWe thank the reviewer for this valuable suggestion to more clearly present the structure-\nproperty relationships for the different spinning strategies. To directly address this concern, a\ncomprehensive figure has been organized to systematically compare the three different spinning\napproaches as shown in Figure R14 (supplemented as Supplementary Fig. 10 in the Supporting\nInformation). It provides a detail mechanism and structure for each strategy and the resulting\nfiber:\nFirst, representative SEM cross-sectional images are provided for fibers produced under each\ncondition in Figure R14a (Supplementary Fig. 10a). These images visually substantiate the\ndistinct microstructures, such as the transition from a uniform porous network to a densified\nstructure or a pronounced hierarchical architecture.\nSecond, a summary table in Figure R14c (Supplementary Fig. 10c) link each spinning protocol\n32\nto its key performance metrics, specifically spinning dope, coagulation bath, porosity and\ntensile strength. The data clearly show increasing the coagulation bath acidity and pre-\nprotonated dope leads to higher porosity but lower initial strength. This consolidated\npresentation offers the clear and direct evidence requested, allowing for an immediate\ncomparison of each spinning strategy engineers a unique structural and mechanical signature\nin the final aerogel fiber.\nIn response to your comment, we have added the corresponding detail data of Figure R14a,\nR14c as Supplementary Fig. 10a, 10c, and supplemented the corresponding descriptions in the\nrevised Supplementary Information:\n“(a) Schematic description of the three strategies of preparation methods for aerogel fiber\nporous structures, with accompanying SEM cross-sectional micrographs revealing the achieved\nporous morphologies. (b) Ashby diagrams of ultimate tensile stress versus porosity of AF\nfiber…... (c) Comparative analysis of the porosity and mechanical strength of fibers produced\nby the three strategies.”\nFigure R14. Engineering three wet-spinning strategies to the fiber’s porous architecture\nand performance properties.\n33\n(a) Schematic description of the three strategies of preparation methods for aerogel fiber porous\nstructures, with accompanying SEM cross-sectional micrographs revealing the achieved porous\nmorphologies. (b) Ashby diagrams of….. (c) Comparative analysis of the porosity and\nmechanical strength of fibers produced by the three strategies.\nQ6: In Figure 1 and Supplementary Table 3, the literature comparison should be updated to\ninclude recent and comprehensive citations. A more complete benchmarking will better\ncontextualize the significance of the reported performance metrics and highlight the\nadvancement contributed by this work.\nOur response:\nThank you for the reviewer’s suggestion. The literature data in Figure 1c and Supplementary\nTable 3 have been updated. We have conducted a thorough literature search and added high-\nimpact publications on aerogel fibers (Ref.: Nano Lett. 2022, 22, 3516-3524; Matter 8, 2025,\n102155; Adv. Funct. Mater., 2025, 2506968; Adv. Fiber Mater., 2025, 7, 1605-1614) to provide\na more comprehensive and up-to-date performance.\nWe have made corresponding modifications and references in the description of the\nIntroduction on Page 3, Line 51:\n“Despite extensive efforts dedicated to enhancing fiber strength from tens of kilopascals (kPa)\nto approximately 70 MPa8-13 (add the Ref.: Nano Lett. 2022, 22, 3516-3524), this is sufficient\nonly for manual weaving and insufficient to meet the demands of complex textile engineering.”\nAdded references in the revised manuscript:\n1. Xue, T.T. et al. Ultra-strong skin-core polymer aerogel fibers via wet-freeze spinning. Matter 8,\n102155 (2025).\n2. Li, Q.H. et al. Tough, Highly Oriented, Super Thermal Insulating Regenerated All-Cellulose\nSponge-Aerogel Fibers Integrating a Graded Aligned Nanostructure. Nano Lett. 22, 3516-3524\n(2022).\n3. Hu, Y.H. et al. Engineering Aramid Aerogel Fibers with Core-Shell Structure for High-Performance\nThermal Protective Textiles. Adv. Funct. Mater. 35, 2506968 (2025).\n4. Yu, Y. et al. High-Strength and Thermal Insulating Polyimide Aerogel Fibers with Porous-Cortex-\nDense-Core Structure Enabled by Hierarchical Phase Separation. Adv. Fiber Mater. 7, 1605-1614\n(2025).\nQ7: Several figures and tables in the Supplementary Information—such as Figure S38 and\nTables S4 and S5—are critical to the overall findings but are not mentioned in the main text.\nsupporting data are properly integrated into the narrative.\nOur response:\nThanks for the reviewer’s comment. It is indeed important that all supporting data are properly\nintegrated into the main narrative. We have reviewed the manuscript and added explicit citations\nand discussions for the previously unmentioned figures and tables to ensure the reader is\neffectively guided. The main revisions in the revised manuscript are as follows:\n(i) A new sentence and citation for Supplementary Fig. 39 have been added in the revised\nmanuscript on Page 13, Lines 262-265:\n“Fundamentally, this high performance is rooted in the selection of heterocyclic aramid\nnanofibers (HANFs), which proved to be a superior nanobuilding block compared to\nconventional Kevlar- and meta-aramid nanofibers for achieving both high strength and high\nporosity (Supplementary Fig. 39 and Text 2).”\n(ii) A reference to Supplementary Table 4 and 5 has been added in the revised manuscript on\nPage 14, Line 276:\n“As a result, HANF-AF achieves a superior strength-porosity balancing feature (Fig.1c and\nSupplementary Figs.10 and 48, detailed parameters in Supplementary Table 4 and 5), which is\nattributed to the uniform hierarchically porous structure and synergistic dense-packed aligned\nstructure with a continuous uniform nanoporous core structure.”\nQ8: The authors may consider moving the entire Figure 2 to the Supplementary Information.\nAt its current placement, Figure 2 provides limited essential data and interrupts the logical flow\nof the assembly/gelation discussion in the main text. Relocating it to the SI would help\nstreamline the narrative while still allowing readers to access the detailed characterization\nif needed.\nOur response:\nWe appreciate the reviewer’s thoughtful suggestion regarding the narrative flow of the\nmanuscript. We have carefully considered this point and re-evaluated the manuscript's structure.\nWhile we fully agree that maintaining a streamlined narrative is paramount, we respectfully\nbelieve that retaining Figure 2 in the main text is crucial for the manuscript’s logical coherence\nand overall impact. We want to provide a detailed and comprehensive overview of our\nreasoning.\nFirst, it establishes the foundational nanobuilding block: The manuscript’s core narrative\nfollows a logical progression: (i) creating the novel nanobuilding block, (ii) controlling its\n35\nassembly, and (iii) characterizing the final material's performance. Figure 2, which details the\nfabrication of ultrafine (3.4 nm) HANFs from recycled sources, represents the critical first step\nin this sequence. As this is a key enabling technology and a central claim of our work, presenting\nit upfront in the main text is essential to frame the subsequent sections.\nSecond, it is crucial for understanding the assembly mechanism: The visual comparison in\nFigure 2b-d, which highlights the exceptionally small diameter of our HANFs versus\nconventional Kevlar-ANFs, is not merely a background characterization. This size difference\nis the fundamental reason why our ion-mediated assembly is so effective and is central to the\n“size effect” discussion that immediately follows in the “HANF secondary assembly” section.\nPlacing this Figure in the main text allows the reader to immediately grasp this critical\nprerequisite for the assembly mechanism.\nThird, it visually anchors the sustainability theme: Figure 2a provides the primary visual\nrepresentation of the closed-loop recycling concept, a major theme of our manuscript. We feel\nthis important framework is most impactful when presented directly in the main text,\nimmediately conveying the sustainability aspect to all readers.\nConsequently, given that Figure 2 provides essential, non-supplementary information that is\nfoundational to the paper's main claims and logical flow, we have opted to retain it in the main\ntext. We hope the reviewer finds this justification reasonable. Thanks again for your suggestion\nand comments.\n36"}, {"round": 2, "reviewer_comments": {"reviewer_1": "Thanks authors for effects on the revisons. Now I recommand this articale to publish on Nat. Communi. without any revisions.", "reviewer_2": "The authors have addressed all concerns raised by reviewers. This revised manuscript should be accepted for publication in Nature Communications.", "reviewer_3": "All my concerns have been satisfactorily addressed, and I recommend accepting the manuscript."}, "author_response": ""}]

Decision letter