The American Society for Testing and Materials, or ASTM, sets standards for sports safety equipment including helmets used in skating and skiing. For basic rollerblading and rollerskating, the ASTM has extended bicycle helmet standards to cover these activities because falls while skating mimic those of biking. Snow sports such as skiing and snowboarding often involve more frequent falls and head-impacts and require a different style of helmet.
Single Impact Helmet
Skating and bicycling helmets are designed for a single impact. When you fall while skating, the initial impact with the ground could cause death if you hit your head hard enough, and these helmets provide the padding and support required to mitigate this risk. If you fall and hit your head while wearing a skate helmet, you need to make sure that you replace it in order to continue keeping you safe in any future falls.
Multiple Impact Helmet
If you've ever gone skiing or snowboarding, especially as a beginner, you know that you spend much of your day on the ground. The regular and repeated impacts with the ground require that you wear a helmet that can support continued blows without diminished safety effectiveness. Choose a helmet approved by ASTM or Snell standards in order to ensure continued effectiveness.
When you look at a ski helmet and a skating helmet, you'll notice that the ski helmet provides more head coverage than a skating helmet. The ski helmet starts at the forehead and covers the ears and the back of the head, all the way to the top of the neck. Some helmets provide a chin bar as well that wraps around the front of the face. In most cases, the helmet thickness is fairly small, providing a close and sleek fit around your head.
The bike helmets used for skating provide less overall coverage and a thicker protective shell making them appear bulkier than ski helmets.