Fogged lenses can be a problem for those of us who like to use their binoculars in cold weather. If you’re not going to use your binoculars in cold weather, then nitrogen-filled binocs aren’t important to you.

Nitrogen-filled binoculars resist getting fogged up inside because they are sealed off from the atmosphere outside. Nitrogen gas provides a constant atmosphere in the sealed tubes of the tandem telescopes that make up a pair of binoculars.

Because each tube is sealed, the nitrogen gas won’t escape and moisture won’t get in. Your lenses won’t get foggy.

It is easier for the manufacturer to produce straight-line roof prism binoculars that are nitrogen-filled than the Porro prism design. Over half of the roof prism binoculars are nitrogen-filled, while barely one-fifth of the Porro prism binoculars are.

Nitrogen-filled binoculars are a mark of quality. Always go for quality when you can afford it.