Stick to decent quality, reputable manufacturers for your glasses. Your eyes are not something to fool around with. If you can get then for $20 they probably are not worth it. Companies like Smith, Oakley, Wiley X, and others put significant testing into their ballistic lenses. I have seen Smith's testing and it is impressive. I am not shilling for any of these over another, but from experience of having a small steel splinter removed from an eye DO NOT CHEAP OUT ON EYE PRO!