A thermal paintball mask simply refers to the type of mask lens. A thermal lens is actually two separate lenses with air in between that help prevent fogging. Some lenses may also be tinted, similar to sunglasses.
Additional factors to consider when purchasing a paintball mask include face and ear guards, padding and fit. A mask should cover the chin and ears. Padding should mold to one's face and return to its original shape after use. Padding should also feel comfortable. A mask should fit snugly and firmly but should not pinch. As of September 2014, paintball masks can be purchased for anywhere from under $20 to over $100.