The practical application of flexible and stretchable electronics is significantly influenced by their thermal and chemical stability. Elastomer substrates and encapsulations, which are characterized by their soft polymer chains and high surface-area-to-volume ratios, are especially susceptible to high temperatures and flames. Overheating can cause substantial damage and decomposition of these elastomers.

Surface treatments for flame retardance have a minimal impact on the overall performance of substrates, as they only introduce flame-retardant ingredients to the surface. However, many flame retardants, such as metal hydroxides and silica, are not suitable for stretchable electronics due to their brittle and non-stretchable characteristics.

Water is widely utilized in firefighting because of its non-flammability, high heat capacity, and high heat of vaporization. For example, a paper cup filled with water is challenging to ignite, even when exposed to a fire source. Similarly, if stretchable devices were to incorporate a mechanism for storing water, they could achieve improved flame retardance and thermal stability. In this study, we suggest an encapsulation strategy based on hydrogels that effectively "locks" water, providing high-enthalpy thermal dissipation for stretchable electronics. This encapsulation method provides significant thermal protection and flame retardance for these devices. Our encapsulated devices exhibit greatly enhanced stability under flame exposure, enduring 10 seconds of burning and dissipating eight times more heat than their original capacity. Furthermore, the stretchability and sensing performance of the flame-retardant devices can be easily restored using desiccants that absorb moisture from the air. This strategy presents a universal approach to improving the thermal stability of stretchable electronics in practical applications.