This is likely due to local overheating caused by oil or grease. Please make sure to observe the recharging instructions provided in the manual. Prevent the bag from coming into contact with grease and oil and only recharge Pingi in a clean microwave-safe dish; do not place Pingi directly on the microwave floor, grate or rotating plate. If you have lost your instruction manual, please download it from the product page on pingi.com.
Discard the defective item after allowing it to cool down.