###### Abstract  
Planar heaters are designed to deliver uniform heat across broad surfaces and serve as critical components in applications requiring energy efficiency, safety, and mechanical flexibility, such as wearable electronics and smart textiles. However, conventional metal-based heaters are limited by poor adaptability to curved or complex surfaces, low mechanical compliance, and susceptibility to oxidation-induced degradation. To overcome these challenges, we applied a protein-assisted electroless copper (Cu) plating strategy to electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber substrates to fabricate flexible, conductive planar heating membranes. For interfacial functionalization, a protein-based engineering approach using bovine serum albumin (BSA) was employed to facilitate palladium ion coordination and seed formation. The resulting membrane exhibited a dense, continuous Cu coating, low sheet resistance, excellent durability under mechanical deformation, and stable heating performance at low voltages. These results demonstrate that the BSA-assisted strategy can be effectively extended to complex three-dimensional fibrous membranes, supporting its scalability and practical potential for next-generation conformal and wearable planar heaters. caption=color=black  
mechanical durability, and are prone to degradation from oxidation, thus limiting their applicability in advanced systems [6; 7; 8]. Accordingly, selecting substrate materials and fabrication processes that simultaneously provide flexibility, durability, and thermal stability is essential. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is a fluorinated copolymer with excellent flexibility, thermal and chemical stability, and high electrical resistivity, making it a promising material to meet these requirements [9; 10; 11; 12]. Furthermore, PVDF-HFP's dielectric properties minimize interference with the conductive layer and ensure thermal reliability under operation [11]. Owing to these characteristics, PVDF-HFP is highly suitable for use in wearable or conformal thermal devices, especially when fabricated into nanofibrous membranes via electrospinning, where it demonstrates excellent potential as a support material for flexible heater applications. The resulting porous, three-dimensional (3D) architecture enhances mechanical compliance and conformability to curved surfaces while providing a favorable matrix for metal deposition [10; 11]. However, due to the inherently high electrical insulation of polymers, achieving thermal functionality requires the formation of a uniform, continuous conductive metal layer throughout the nanofiber network. Electroplating is a widely used technique that allows for precise control of coating thickness through the application of external current, offering distinct advantages in microfabrication processes. However, this method requires electrically conductive substrates to sustain current flow, and the inherent non-uniformity of current density within the plating bath can result in uneven coatings on complex geometries [13; 14; 15]. In contrast, electroless plating enables uniform metal deposition without the need for an external power source, making it more suitable for coating insulating and geometrically complex substrates such as electrospun nanofibers. While electroless plating has become a widely adopted strategy for metal functionalization of polymer-based flexible electronics, conventional methods often rely on Pd/Sn catalysts, plasma treatments, or polydopamine adhesion layers. These processes are typically optimized for flat substrates and suffer from limitations such as the need for vacuum systems, toxic reagents, and prolonged processing times [16; 17]. To address these limitations, protein-based surface pretreatment strategies have emerged as promising alternatives, with bovine serum albumin (BSA) being one of the most extensively studied examples [17]. BSA contains amine, carboxyl, and thiol groups that enable strong coordination with Pd\({}^{2+}\) ions.