In this video Freddy helps you understand the different mask technologies and gives some pointers on how to get the correct fit for a snorkel mask and dive mask.

How to Buy the Right Scuba or Snorkel Mask Revisited In Depth:    • How to Pick the Right Snorkel or Dive...  
A more complete, indepth dive into picking the right mask.

How to Buy the Right Scuba or Snorkel Mask Revisited Less Detailed:    • How to Pick the Right Snorkel or Dive...  
Completely different video that contains the same basic info, but doesn't go into as much detail.