It is a promise that the heat patch will maintain the heat for 4 to 6 hours. It functions perfectly after that promised date. 4 to 6 HOURS OF HEAT: Sunny Bay’s self-adhesive, air-activated body heating packs provide up to 100 ºF of safe heat to relieve muscle pain, soreness, and tension caused by intense training or menstrual cramps that can happen during daily activities. No microwave necessary - simply activate it right out of the package for the best thermal therapy for your aching body. SELF ADHESIVE: Our stick-on patches are a convenient way to relieve chronic pain and they stay put! Simply place the patches inside your clothing adjacent to the affected pain areas. They immediately go to work to increase blood circulation, loosen tight muscles, and soothe period cramps. AIR ACTIVATED: Sunny Bay air-activated heat pads the most effective way to relieve pain during your busy day at work, school, or on the go. Keep them in your purse, gym bag, or backpack for instantly accessible relief from muscle aches, cramps, and strains. COMFORTABLE: Each pack is covered in a premium soft-touch woven fabric that conforms to your body shape. Whether you’re standing up or moving around in your office chair, the pack stays put. They provide heat for up to 6 hours when applied and are designed to protect your skin from the long-lasting heat stored inside. You’ll feel better in practically no time! DISPOSABLE: No need to save them! These heat wraps are designed to provide you with soothing relief from muscle aches and pains, and then be disposed of with ease. They’re odor-free, you don’t have to wash them, and you can buy as many as you like for instant treatment when you need it most. Size: 5" x 5"