Make sure the product is correctly assembled:

For Urban Air Mask 2.0 see:
For Lite Air Mask, see:

When the mask is put on, the nose foam should end up on your nose. Behind the nose foam, the mask has a built-in shapable nose-clip. Follow the video linked below and form the nose-clip and nose foam after your nasal shape. The nose-foam creates an airtight seal to reduce hot and moist air to leak out and fog your glasses. Finally, put your glasses just over the top of the mask. This will reduce fogging even further.