Fiberglass or Urethane Chin Spoiler?

Urethane will require special paint additive, but will not break/crack if bumped.

im with t5 on the breaking/cracking part.the urethane one is WAY more forgiving than the glass.as far as the "addtive"goes the small amount of flex that the painter/you will be adding to the primer/sealer&clear,its a small amount and and wouldn't really be a deal breaker as far as final cost is concerned.its only there to aid in the install of the part,you won't be able to tie it in a knot and not have the paint crack.i'd go with the urethane one those parking lot curbs are not friendly ](*,)

+1 for urethane

All depends what your doing with the car. The poly spoiler is better for a street car. Because it is flexible, imagine what its doing at highway speeds. Personally running a fiberglass spoiler.