The Cool58 Standard Pack Set includes four (4) 6" x 13" packs for the Cool58 Zipper or Poncho Cooling Vests. Cool58 Standard Pack Set includes: Four (4) 6" x 13" Cool58 Packs Each pack weighs 1.1 lbs. (500g of cooling material) for a total vest weight of 5.0 lbs. How does it work?: These cooling packs freeze solid at a comfortable 58° Fahrenheit, so they can be frozen in a freezer, refrigerator, or even a bucket of ice water. Once activated, these reusable packs deliver comfortable cooling for up to 2-3 hours. (Please note: cooling times are estimates and will vary depending on climate, body metabolism and activity.) Packs are non-toxic and non-flammable. Packs do not require a freezer! Packs can simply be submerged in ice water or placed in a refrigerator or freezer to activate. The cooling performance is not impacted by humidity or outside temperature. Polar Products Extra Set of Cool58 500 Gram Standard Vest Cooling Packs, Pack Set 4