Adjust the strap. Most diving mask retaining straps are made of silicone rubber, which is flexible and soft. If you go snorkeling, the snorkel will be attached to this strap. Some people find that long hair gets badly tangled in silicone straps, so they look for a mask with an elastic strap. Whether the strap is elastic or silicone, make sure it has a comfortable width and adjusts easily to the size of your head. You know it's adjusted well when it stays in place when you shake your head but doesn't feel uncomfortably tight.