Don't buy these until you've tried the other techniques it the book... this is where things can get dangerous.
Sub-Categories

Deep Heat Pain Relief Heat Patch, Muscular Aches, Pains, Joint Stiffness (Pack of 4 Patches)
4.0

KETOTEK Seedling Heat Mat, Seed Heating Mat Plant Warming Pad 220V Seed Germination Heat Mat Waterproof 21W
4.0

From Zero To Heat Pump Hero: Maximise Comfort and Efficiency: Your Guide to Understanding Your Air Source Heat Pump
4.0