These are cold packs that are filled with a non toxic gel and frozen before shipped. One pack will keep yeast cool for up to 6 days in transit. We recommend one of these for every 4- 6 yeasts, especially in the hotter months. These packs are FROZEN when shipped, thus we recommend you purchase no more than 1 Gel pack for every 3 yeast ordered. The yeast may freeze if packed with too many gel packs. To prevent freezing we will pack excess ice packs that may have been ordered in another part of the parcel if necessary. We include one free gel ice pack with every order of liquid yeast. Purchase additional packs if needed. These ice packs can be reused dozens of times; simply re-freeze and they are ready for an ice chest or other application.