Enhancing Comfort\nand Functionality in Stretchable\nThermotherapy Thin\nFilm Heaters through Breathable Design

Stretchable thin film heaters (TFHs) are essential for\nlocalized\nthermotherapy, conforming to the skin and joints. However, conventional\nTFHs made from nonbreathable elastomers often cause discomfort and\nincrease infection risks. We propose a sample TFH design that is both\nbreathable and stretchable. By using nickel (Ni) foam as a sacrificial\ntemplate, we deposit Ag nanowires (Ag NWs) to form the heating element,\nwhich is then encapsulated in polydimethylsiloxane (PDMS). Crucially,\nthe PDMS coats only the inner surfaces of the micropipes, leaving\nthe interstitial spaces unfilled, creating a breathable 3D conductive\nnetwork. This contrasts with traditional TFHs that are typically nonbreathable\nand limited in flexibility, often leading to heat accumulation and\ndiscomfort. Our TFH maintained consistent performance over 1000 cycles\nof bending, stretching, and water immersion. Even with up to 25% stretching,\nresistance changes remained under 13%. Breathability tests revealed\na 5:1 ratio in deionized water permeability between an uncovered bottle\nand one covered with our film with a permeation rate of 7 mg/cm<sup>2</sup>·h. Also, the TFH effectively reached 67 °C within\n1 min under a 3.5 V bias. Unlike existing methods that neglect breathability\nor require complex fabrication, our strategy offers a simple yet robust\nsolution to the limitations of conventional TFHs, combining both breathability\nand stretchability.