Clear bra is made to withstand rock chips and even some small road debris from damaging your car’s paint. That being said, it is still a thin piece of plastic sitting at (8 mils in thickness). Throw anything big enough or hard enough at it and it will go through the clear bra and onto your paint. 

We have seen some scenarios where clear bra has protected a car’s paint after grazing a mailbox or even another car, but the amount of damage clear bra can withstand is relative to the size and the force behind the object in question.