These HD filters use specially hardened glass that is far more resistant to breakage than other optical glass.
Hardened Glass... Hardened optical glass that has 4 times the breaking strength in ANSI standardized testing (ANSI Z80.3 : 2001) where steel balls of varying size and weight were dropped from a height of 50 inches onto the glass.
Reviewed by 1 customers
This Hoya HD clear protector is the strongest glass out there for its minimal thickness, and it offers the best protection for the least loss. It is a bit pricey, but you will only have to buy it once since they last almost forever. If you choose your camera, and more importantly your lenses with picture quality in mind, what sense does it make to screw on a lesser filter? Read about filters on [@] as he offers excellent consumer information for free, and consider supporting his site with your click through purchases at no added cost to you.