Polymers is a category of materials that includes polyvinyl chloride (PVC), polytetrafluoroethylene (Teflon), polyethylene (PE), polystyrene (PS) and many others. Plastics and elastomers are types of polymers. Materials in this category are typically low in density, low in cost, and have great versatility in form, function, and aesthetics. Polymers can be clear, translucent, or opaque. They are electrical and thermal insulators. Though polymers are generally not as strong as metals, they are often reinforced with glass or carbon fibers to increase their strength.