For snowboard you want a helmet with no holes, and ear protection, even when hot, snow will get in ears and is a pain, also snow melts so if it gets in holes it makes your helmet wet inside. Nice to have is a short one inch front ledge, if you are landing on your face that bit will hit the ground before your nose, I purposely turn my head into the fall to make it happen. Better a hit in the higher part of the face and helmet than landing jaw or nose first, is as bad as it sounds. It needs to be shaped in a way that doesn’t impede your goggles, no sun shader so you have a better field of view upward, in some jump tricks you need to look upward. Need to stop hits on ice at high speed and slide, smoother helmet surface is better. Hits come from any direction, including the rear of the neck, so the helmet cover the sides and the rear a lot. Finally it’s likely to be fitted with a plastic clip in the back to retain your goggles strap so when you hit hard goggles don’t fly away.

For bicicle you want a lot of holes to cool you down, nothing blocking your ears cause that’s where your sunglasses sticks go. Sticks go outside the helmet lace cause it harms less if you fall. Need big long sun shade so the sun won’t cause reflections on your sunglasses, you will not need to look upward aniway. But left-right it need a to give a good field of view. Need to stop car hits for life saving purposes, no need to protect the face as yo are not looking for continuous hits. Instead, it’s focused for the centerline hits, front, top, upper rear. Its way deeper in protection compared to a snowboard one.

For downhill bikes you want a full face helmet because tooth and face surgery is expensive. It needs to stop the big hits but also prevent the continuous face scratching done by tree branches, and light hits to the ground in light falls. It is generally designed to be connected to neck protection too.

To close it: street bike helmets can be one shot, you hit, you discard the helmet. This allows lighter and softer designs, and a in depth protection; that single hit will hurt less that in a reusable helmet. Most extreme sport helmets can retain shape after multiple light hits. If I had to replace the snow helmet every hit, I would be broke. This comes at the cost of the helmet being a bit more rigid, giving less comfortable, sharper hit feeling, and more weight.