Formula 409, and now my mirror doesn't fog?

I cleaned the apartment earlier this week, and being out of glass wipes, I shrugged and just sprayed Formula 409, an all-purpose cleaner, on my mirror and wiped it with paper towels.

Now my mirror doesn’t fog when I’m in the shower, even when I fire up the hot water and leave it running to use the sleepy man’s iron (steaming clothes to relax the wrinkles).

Why is this? Is it dangerous for the mirror? If not, why don’t more people do this, or do they and I just figured it out by mistake?

I think that you managed to get it very, very clean and there is no place for the water to cling. Once dust and grime starts to build up, you’ll get a foggy mirror again.


WAG; if you spread a very thin film of soap on glass, it won’t fog up (but it looks slightly milky, because, well, it’s soap.) Maybe 409 leaves a similar film behind on the glass that prevents fog from accumulating?

I once used 409 on my windshield. It left such a bad film that I had to replace the windshield because I could not get film the off.


I used the same stuff on a mirror too (expcet the orange formula) and it did the same thing - the mirror didn’t fog. But after about a week, it resumed to it’s foggy self again.

Filing this information away under “Really Useful Things to Know That You Usually Only Learn By Accident”

Reminds me of the time that my friend defrosted his windshield using a pitcher of hot water.

Here, I thought being born in Buffalo gave everyone an instinctive sense that that was a Bad Thing.

I routinely use 409 on my windshield, and have never had problems with film. Of course, once you’ve gotten the worst crud off with 409, you have to take the excess 409 off with windex.

Mirrors and windows “fog” because condensed water forms a layer of very tiny droplets that scatter light. If you have a trace of soap on the mirror, the surface tension is altered and the droplets form a continuous film of water which doesn’t scatter light, so the mirror doesn’t appear fogged (although it is wet.) Which is useful if you use a CD as a shaving mirror in the shower. It’s much the same reason why ice made with boiled water is clear, ice made with non-boiled water is cloudy, and snow is white.

(“Swimmers and soap” experiment - scatter pepper across the surface of a glass of water, then dip the corner of a bar of soap into the middle and watch the pepper all scoot to the edges as the surface tension breaks! Or take my word for it, it’s not that exciting.)

I guess Formula 409 has a similar effect on water surface tension but it sounds rather longer lasting than soap. I know some guys use glycerin to stop their goggles misting up when paintballing - maybe Formula 409 works better. Can I get some this side of the Atlantic?