# Is it true that your glasses won't fog up if you go in from the cold backwards? **URL:** \ **Category:** Factual Questions\ **Created:** [January 14, 2009, 10:41pm UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338 "2009-01-14T22:41:00Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![wigwag](https://avatars.discourse-cdn.com/v4/letter/w/f1d935/32.png) [@wigwag](https://boards.straightdope.com/u/wigwag)\ **Post date:** [January 14, 2009, 10:41pm UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/1 "2009-01-14T22:41:00Z")
I know this sounds goofy but CBC radio just said it was so. It’s a delightful minus 20 here… ---
**Author:** ![Valgard](https://avatars.discourse-cdn.com/v4/letter/v/7feea3/32.png) [@Valgard](https://boards.straightdope.com/u/Valgard)\ **Post date:** [January 14, 2009, 10:46pm UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/2 "2009-01-14T22:46:04Z")
I have not done a scientific study of it but I call BS. I wear glasses and they will fog over rightside up, upside down, backwards and any otherwards. It’s just condensation - lenses are freezing cold when you’re outside, you walk in where it’s nice and warm, water vapor in the air will condense on the cold surface. ---
**Author:** ![JSexton](https://avatars.discourse-cdn.com/v4/letter/j/96bed5/32.png) [@JSexton](https://boards.straightdope.com/u/JSexton)\ **Post date:** [January 15, 2009, 12:40am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/3 "2009-01-15T00:40:21Z")
Sounds like something that would circulate via emails of STRANGEBUTTRUE! facts, which are generally strange and false, like a duck’s quack not echoing. It’s 20 below where you are? Then walk outside and test it for yourself. ---
**Author:** ![Fish](https://avatars.discourse-cdn.com/v4/letter/f/bc8723/32.png) [@Fish](https://boards.straightdope.com/u/Fish)\ **Post date:** [January 15, 2009, 12:45am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/4 "2009-01-15T00:45:25Z")
It’s true, they don’t fog up if you walk inside backwards. But it only works in the vacuum of space. ---
**Author:** ![ivan\_astikov](https://avatars.discourse-cdn.com/v4/letter/i/58f4c7/32.png) [@ivan\_astikov](https://boards.straightdope.com/u/ivan_astikov)\ **Post date:** [January 15, 2009, 12:45am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/5 "2009-01-15T00:45:53Z")
No, but it is true that if you close your eyes, you wont notice it. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 15, 2009, 12:49am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/6 "2009-01-15T00:49:05Z")
it works like this: you walk backwards in through the door, you trip over the door jamb, fall backwards and fracture your skull on the hall floor - when you regain consciousness after lying in a coma for three months, your glasses aren’t steamed up. ---
**Author:** ![mswas](https://avatars.discourse-cdn.com/v4/letter/m/e99b99/32.png) [@mswas](https://boards.straightdope.com/u/mswas)\ **Post date:** [January 15, 2009, 12:50am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/7 "2009-01-15T00:50:23Z")
Well there is the idea of your breath getting blown back into your face and that fogging up your glasses. If your breath blows further from your face, maybe then it won’t fog up your glasses? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 15, 2009, 1:01am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/8 "2009-01-15T01:01:23Z")
I doubt that’s a significant factor. The lenses get chilled and condensation form on them when you go indoors, because there is sufficient moisture in the air to condense on the cold surface. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [January 15, 2009, 1:24am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/9 "2009-01-15T01:24:10Z")
You must not be from a cold climate. They fog up regardless of direction of travel from cold to warm. The only way they won’t fog is to have them inside your coat where they stay warm. ---
**Author:** ![wigwag](https://avatars.discourse-cdn.com/v4/letter/w/f1d935/32.png) [@wigwag](https://boards.straightdope.com/u/wigwag)\ **Post date:** [January 15, 2009, 1:44am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/10 "2009-01-15T01:44:07Z")
> [@](#): > > You must not be from a cold climate. HD, are you talking to me? Just how cold _is_ it in Wisconsin anyway? ---
**Author:** ![Manduck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manduck/32/256_2.png) [@Manduck](https://boards.straightdope.com/u/Manduck)\ **Post date:** [January 15, 2009, 1:48am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/11 "2009-01-15T01:48:03Z")
> [@mswas](#): > > Well there is the idea of your breath getting blown back into your face and that fogging up your glasses. If your breath blows further from your face, maybe then it won’t fog up your glasses? They will fog up from that cause when you are still outdoors. Walking backward might actually help with that. ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [January 15, 2009, 1:51am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/12 "2009-01-15T01:51:02Z")
Just popping in to say I heard this perhaps 15 years ago. Definitely before most people would have sent an email. I can’t supply more info than that. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [January 15, 2009, 2:44am UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/13 "2009-01-15T02:44:02Z")
> [@wigwag](#): > > HD, are you talking to me? Just how cold _is_ it in Wisconsin anyway? Right now a couple degrees below zero. I would have expected a person in a cold climate to have put on glasses and tried this, even if it’s a pair of sunglasses. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 15, 2009, 11:33pm UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/14 "2009-01-15T23:33:51Z")
Sunglasses might not work if the lenses are thin plastic - they don’t have a lot of thermal mass. I would have tried it, except for the fact that the weather has turned mild here the last day or two. Last week it was minus ten and my glasses were steaming up every time I came home. I even got into the habit of taking them off in the garage so I wouldn’t trip in the hall when they steamed up. They still steamed up even when I was just carrying them. Cold lenses + warm comparatively humid house = condensation. Walking backwards isn’t going to make a difference. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [January 15, 2009, 11:42pm UTC](https://boards.straightdope.com/t/is-it-true-that-your-glasses-wont-fog-up-if-you-go-in-from-the-cold-backwards/481338/15 "2009-01-15T23:42:02Z")
It was ten below this morning by our thermometer. The official temps were colder than that. It was so cold that my lens were falling out of the frame, so I let them warm up in the house and reassembled them. I’d actually forgotten that the lenses shrunk enough in sub zero weather to do that.