This pack contains 2 Self-heating Pain Relieving Small/Medium Thermacare Back Wraps for waist sizes up to 34". ThermaCare heat wraps are made of soft layers of cloth-like material with patented heat cell technology that contain natural heat generating ingredients (iron charcoal table salt and water). When exposed to oxygen in the air these ingredients react to produce heat. Thermacare pain relieving heatwraps provide effective relief of muscular and joint pains associated with overexertion strains sprains and arthritis. ThermaCare gets warm and stays warm delivering constant long lasting therapeutic heat for at least 8 hours.