When buying a dive mask, what are the key elements to consider?

Scuba masks come in different styles, designs, and materials but for the best vision and highest level of comfort, it would be important to consider certain elements.  For starters, a mask with a silicone skirt would reduce risk of allergic reaction over a skirt made from plastic, rubber, or latex.  Additionally, the size of the nose pocket should be snug but not too tight.  That way, the nose is protected and cushioned while keeping the lens from fogging over.  For strap, single is fine but a double strap is beneficial in that it can be adjusted in two places for better comfort and more stability.  You can even order a prescription dive mask to eliminate the need for wearing glasses or contacts.