The vast majority of snowboard helmets use EPS foam which is generally rated for just one significant impact, meaning you should replace it after any substantial hit. There are a few exceptions, with new stuff being developed all the time. A few companies offer multiple-impact protection, but some of them are technically not even helmets (e.g. Bern's "Hard Hats"). Besides Bern, Protec and POC come to mind. I think POC has some that are technically helmets, but still rated for multiple (smaller) impacts while still meeting helmet safety standards (ASTM F2040, CE EN1077, etc).