These packs help alleviate pain and swelling instantly. No refrigeration is needed, just squeeze to activate each single-use pack. Water blends with ammonium nitrate, absorbing heat and lowering the pack's temperature instantaneously. Each pack stays cold for 15 to 20 minutes. One time use for these packs means there is no risk of cross contamination or any need for disinfecting packs after use. Each pack measures 6" x 9".