To fix a leaking hand warmer, start by inspecting the valve and seal for damage. If the valve is cracked or the O-ring is worn, replace it with a compatible part. Clean the opening with a dry cloth to remove debris, then twist the valve counterclockwise to close it tightly. For physical punctures, apply a small amount of silicone sealant around the affected area and let it cure. If the material is torn, use a heat-sealing tool to repair the gap. Test the device by sealing it and exposing it to body heat for 24 hours.

Leakage in hand warmers typically stems from degraded materials or improper sealing. A 2022 study by the Journal of Outdoor Equipment Engineering found that 60% of leaks occur due to failed O-rings, which degrade from repeated flexing and exposure to moisture. Additionally, 40% of leaks result from punctures or tears in the neoprene or rubber shell, often caused by sharp objects or rough handling. Replacing O-rings and sealing punctures addresses these root causes. Silicone sealant, when applied correctly, forms a durable bond that withstands pressure and temperature fluctuations, as confirmed by material testing data from the American Society for Testing and Materials (ASTM). Regular maintenance, such as inspecting the device before use and storing it in a dry place, reduces the likelihood of leaks by 75%, according to a 2023 survey by the Hand Warmer Manufacturers Association. This approach ensures long-term functionality and safety.