Our heat packs stay warm for over 72 hours. They should keep your plants from freezing during transit in the cold winter months We add 3 or more heat packs in each of your boxes to keep your plants warm during transit. If average daytime temperatures in your area drop below 50 degrees F, we recommend getting a Winter Protection Package. If you're in a cold area, PLEASE add this item to your order to ensure your plants arrive in the best condition possible Also, please note that these heat packs will be opened and activated prior to shipment, and will be mostly used up by the time you receive the order. These are NOT meant for resaleIf you'd like to purchase some unopened, ready-to-use heat packs for your own shipments or other various purposes, check out our listings for ready to use heat packs by searching for "Heat Pack USA" on our product list!