Zovirl Industries

Mark Ivey’s weblog

HOWTO: Use science to stop your mirror from fogging

A simple trick to keep your bathroom mirror from fogging up when you take a shower: get a little bit of soap on your hands, add a little bit of water, and rub it onto the mirror.  Try not to rub it around so much that it makes a lot of bubbles, you just want a thin film of soap on the mirror.  If you do it right, the soap film will be very clear so you won’t be able to tell it is there.  If it is a little blurry, try breathing on it to see if it clears up.  Once you have this soap layer, the mirror shouldn’t fog anymore.

Why does this work?  On a clean, non-soapy mirror, the warm moist air from the shower causes condensation on the mirror.  The water condenses into super tiny droplets that refract the light as it reflects off the mirror, preventing a clear reflection.  However, when there is a thin layer of soap on the mirror, it prevents the water from forming droplets.  Instead, the water that condenses stays in nice flat sheets and doesn’t interfere with the light.  The result is a clear reflection.

Yay, science!

(You can also use this to keep your glasses from fogging up when you exercise in cold weather.  My father showed me this trick years ago when we were cross country skiing.)