Does the mat produce FIR rays when not plugged in? If so, how does it compare to when it is plugged in?

Just like with negative ions, the crystals continue to generate FIR rays even when the mat is unplugged.

When the mat is not powered, the crystals use the warmth of your own body. Your body heats the crystals, and once they become warm, they emit infrared rays in the so-called “crystal” wavelength range between about 4 and 15 microns.

Amethyst concentrates most of the heating energy around two peaks, approximately at 7 and 12 microns.

Naturally, the more heat the crystals receive, the more energy they emit. When the mat is heated by the electrical system or warmed by the sun, the crystals become hotter and release more energy, although the wavelength range remains the same.

This does not mean the mat should always be used at the highest heat level. Unpowered use or lower temperature settings are usually safer and more gentle.