ThermaCare Heat Therapy Muscle Patches deliver continuous low-level heat for up to eight hours to penetrate deep into muscle and joint tissue for lasting pain relief. Each air-activated patch requires no electricity, heating automatically when exposed to air and conforming to body contours for seamless wear under clothing. Clinically proven to relax muscle spasms, increase local circulation, and reduce stiffness associated with arthritis and overexertion. Ideal for back, neck, shoulder, and menstrual pain.