You don't have to ski the trees or catch big air to appreciate a helmet. All skiers and riders can enjoy the benefits and warmth that a helmet provides. Just like running shoes differ from hiking boots, snow helmets are different from bike or skateboard helmets. They have specific features such as ear coverage, moisture-wicking liners and temperature-sensitive materials.
The shell, or outer layer of the helmet, is a rigid surface that can help protect the head against sharp objects, knocks and abrasions. It also helps spread impact energy over a larger portion of the helmet during a fall. Inner liner is typically made from foam. It's designed to absorb impact. In a hard fall, the liner foam can get compressed, a condition that you may or may not be able to discern. A helmet should always be destroyed and replaced after a serious fall.
A good helmet should feel snug but not tight. If the helmet can rock back and forth, the fit is too loose. Shake your head from side-to-side. If the helmet shifts, try a smaller size, adjust the sizing mechanism or use thicker sizing pads. Push up the front and back edges. If they move, tighten the straps. There should be no gap between the top of your goggles and the helmet. Make sure the helmet fits snugly to the top of the goggles, but not so low that it hinders vision or pushes down the goggles. The helmet should be positioned low enough in the front to protect your forehead.