Infra-Red heat, because it is able to penetrate 1 1/2 inches below the skin, causing the body to sweat at a temperature of 110 degrees F - 220 degrees F.
(it; is; able to penetrate 1 1/2 inches below the skin) (it; to penetrate; 1 1/2 inches below the skin)
it it
is to penetrate
able to penetrate 1 1/2 inches below the skin
1 1/2 inches below the skin