Shatterproof Gls bulbs are coated with a clear rubber silicone paste or FEP material over the glass of the gls bulb to make the lamp shatterproof
This material will keep all the glass particals contain in the gls bulb if broken
FEP gls bulbs are usually applied on high wattage bulbs.
This material will last the life of bulb.
Approxamently 1% of light will be lost through the protected coating.