I have a perfectly good motorcycle helmet (one that encompasses the whole head, including the chin) that I never use (I bought it for lessons, but never bought a motorcycle). However, I do not have a skiing helmet and have to borrow one each time which costs money and is not as hygienic as I'm really comfortable with.
So I wondered why I (on the level of a skiing beginner!) couldn't just use the one I own. However I remember reading on some SE site (possibly here, I don't remember and cannot find the post) that not all safety helmets can be worn interchangeably. For example, a bicycle helmet shouldn't be worn for climbing — but I don't think falling down on snow (repeatedly) would be the same as being hit by falling rocks. Also a motorcycle helmet is significantly different from a bicycle helmet.
Motorcycle helmets should not be used as a replacement for a ski helmet:
Most motorcycle helmets weight between 1,000 and 2,000 grams, while ski helmets weigh between 330 and 600 grams.
You are expected to fall repeatedly with ski helmets (on the order of up to several times a day), so it needs to be lighter to not exact an additional toll on your neck
You don't have rear-view mirrors when skiing, so being able to effortlessly turn your head is key
I'm sure there are many more differences, but the weight and freedom of movement differences alone should be enough.Tweet