Frank Lloyd Wright March Balloons Hot/Cold Pack100% organic cotton filled with flaxseed To Heat: Microwave for 60 90 seconds in 30 second increments checking for desired temperature. To help with the life of your pack, you can place a mug of water in the microwave next to the pack to create humidity and prevent dryout. To Cool: Place packing a plastic bag and place in freezer for at least one hour. For added relaxation place a few drops of your favorite essential oil on the pack and rub in.