Paintball masks come in two basic varieties, dual or single pane. Dual pane masks are frequently called thermal lens goggles because the second lens provides a degree of insulation, similar to a storm window, which can also help combat fogging. Dual pane goggles are usually more expensive, but most players find the benefits outweigh the modest outlay. If you're considering playing anything but infrequently, you might want to consider buying thermal. Thermal lenses also come in many varieties, from the sleek speedball tournament varieties to masks that are better suited to woodsball.