Tools
Match the Product to the Moment.
The practical details decide this more often than the technology does.
Answer three questions about how you would actually use it. We will not tell you whether to use heat or cold — that depends on your situation, and it is a question for a professional.
Using either safely
Never apply heat or cold directly to skin, and do not sleep with a heat product in use. Follow the manufacturer's instructions, which override anything general said here.