When I was labouring on building sites as a student (1990 or so), the "cool" thing to do was to take the silver tape used for edging computer flooring tiles, and cover your hard hat in it. I should imagine the tape adhesive didn't much enhance the strength of the underlying plastic, but least you had a cool, shiny silver hat.
When I was a conscript in the Swedish army in the early 90:s, this involved some work around masts and telecomms towers (I was in a signals unit) and, under peacetime labour protection rules, that meant wearing an approved hard hat. The army's steel helmet (m/37, i.e, 1937 pattern!) wasn't approved, so we wore standard, bright orange, hard hats, which looked rather funny with our camouflage uniforms. Someone asked whether we could spray paint them dark green, but the answer was a blank no; they must not be modified in any way or the approval would no longer be valid, and our superiors would be in violation of all sorts of laws for allowing us to use them.