## 2 Materials and Methods  
### Materials  
The subjects of the research were PCM macrocapsules (Microtek Laboratories, Moraine, OH, USA). The macrocapsules were spherical in shape, with a diameter: 4 \(\pm\) 0.5 mm. According to the manufacturer's information, the outer shell of the macrocapsules was polyurethane (PU), while the PCM material was n-octadecane. Based on high-resolution X-ray tomography, micro-CT (SkyScan 1272; Bruker, Kontich, Belgium), and scanning electron microscopy, Nova NanoSEM 230 (FEI, Eindhoven, The Netherlands), the internal structure of macrocapsules was characterized. Both applied techniques showed that PCM macrocapsules are formed from multiple PCM microcapsules (with maximum diameter of about 50 \(\upmu\)m); moreover, PU, which constitutes 21% of volume of the macrocapsule, forms both the outer shell of the macrocapsules (with maximum thickness of 155 \(\upmu\)m) and the outer shell of the microcapsules. The remaining 79% of volume of the macrocapsule is n-octadecane. Figure 2a presents a micro-CT image of macrocapsule's cross section and the SEM cross-section image of macrocapsule's interior with visible microcapsules. As a reference material for the tested PCM macrocapsules, macrogranules of similar geometry made of PP were used (the obtained cross-section image using micro-CT was presented in Figure 2b). Both PCM macrocapsules and PP macrogranules are characterized by low porosity. In the case of macrocapsules, air (white color) constitutes 4% of their volume, filling microopes of a maximum size of 175 \(\upmu\)m. In the case of macrogranules, air constitutes 3% of their volume and fills the micropores of a maximum size of 65 \(\upmu\)m. As can be seen in the presented cross sections, the spatial distribution of pores is more homogeneous in the case of PCM macrocapsules. N-octadecane used as PCM in the tested macrocapsules is characterized by a melting temperature of 28 \({}^{\circ}\)C, heat of fusion of 185 J\(\cdot\)g\({}^{-1}\), with specific heats of 1.9 kJ\(\cdot\)kg\({}^{-1}\cdot\)K\({}^{-1}\) (solid phase), and 2.2 kJ\(\cdot\)kg\({}^{-1}\cdot\)K\({}^{-1}\) (liquid phase). Since the aim of the work was to test the thermal insulation properties of PCM macrocapsules for potential use in thermal protective clothing, an insert containing a monolayer of these macrocapsules (arranged next to each other wrapped in white polyester mesh) was created. Additionally, reference insert containing PP macrogranules was made. Photos of both inserts are shown in Figure 3, while their structural and thermal parameters are presented in Table 1.  
Figure 2: Cross section of PCM macrocapsule **(a)**, and PP macrogranule **(b)**. As can be seen in Figure 3, both inserts were approximately 5 cm \(\times\) 5 cm large and consisted of about 160 macrocapsules/macrogranules. The PCM macrocapsules were opaque white, while the PP macrogranules were colorless. Thermal barriers in protective clothing are most commonly made of nonwoven fabrics. In their place, a PCM insert was used, in two multilayer textile assemblies (\(A\) and \(C\)), due to its high usefulness in thermal insulation systems. As references for assemblies \(A\) and \(C\), assemblies \(B\) and \(D\) were created, respectively, identical in terms of the structure of all layers, except for their thermal barriers, where instead of PCM macrocapsules inserts, inserts with PP macrogranules were used. All four assemblies, the full characteristics of which are presented in Table 2, consisted of four basic layers: (1) outer shell, (2) moisture barrier, (3) thermal barrier, and (4) lining. The outer shell is most resistant to mechanical impact and protects the wearer against hot and toxic substances. The moisture barrier provides protection against the permeation of water and other liquids, including volatile chemicals that could penetrate the outer shell. The moisture barrier also provides a key role in the breathability and insulation of the entire multilayer assembly.