Passive Daytime Radiative Cooling Enabled by Bio-Derived Ceramic-Polymer Coatings on Rapid-Curing Fiberglass Casts

TL;DR

This paper introduces a biocompatible, flexible radiative cooling coating made from bio-derived ceramics on fiberglass casts, achieving significant cooling effects by reflecting sunlight and emitting infrared radiation, suitable for wearable and curved surfaces.

Contribution

The study develops a novel bio-derived ceramic-polymer coating for flexible substrates, enabling passive cooling on conformal surfaces like fiberglass casts, combining sustainability with high optical performance.

Findings

Over 90% solar reflectance achieved

Up to 15°C cooling below ambient temperature

Effective on flexible, curved substrates

Abstract

Passive daytime radiative cooling (PDRC) provides an energy-free approach to suppress surface temperatures by reflecting solar irradiation while emitting thermal radiation through the mid-infrared atmospheric window. Despite rapid progress in optical performance, most PDRC systems remain limited by rigid, fragile, or planar substrates, restricting their use on flexible, curved, or wearable surfaces. Here, we report a biocompatible and structurally robust PDRC system integrated onto a commercial rapid-curing fiberglass cast, a conformal substrate widely used in orthopedic and industrial applications. The cooling architecture adopts a bilayer polymer design consisting of a polyvinyl alcohol (PVA) adhesion layer and a polymethyl methacrylate (PMMA) protective layer, both embedded with calcium pyrophosphate (CPP) ceramic particles derived from processed animal bone waste. The bio-derived CPP simultaneously enables broadband solar scattering and high mid-infrared emittance, while offering sustainability and biocompatibility advantages. The resulting composite exhibits over 90% solar reflectance and achieves up to 15 C sub-ambient cooling under direct outdoor sunlight.