Thermal rags are made from open-weave cotton, which makes them highly absorbent and durable. They are a heavier weight than a standard cotton towel, makingWhite Thermal Rags Thermal rags are made from open-weave cotton, which makes them highly absorbent and durable. They are heavier than a standard cotton towel, making them ideal for situations where maximum absorbency is needed them ideal for situations where maximum absorbency is needed.