Back in the days I worked in the oil fields hard hats were aluminum (I guess plastic hadn't been invented yet). The best thing I can tell you is that a hard hat is pretty much designed to protect you from bumps on your noggin' if you happen to walk into a low beam or something. If someone drops an 18" pipe wrench from 90 feet up and it hits you, it is gonna do some damage, hard hat or not. Personally, if I had to wear a hardhat today I think I would look at one of the cowboy hat versions. Cowboy is cool ya know...