Hi again,
I’ve tried so many different products that claim to elimanate fog from my windows. At first I thought only that it was b/c my windows were dusty or not “squeaky clean”, but after cleaning them almost obsessively it still didn’t help much on my drive back home from Florida. Then I researched the science behind fogging/precipatation. So turning the heater on solves things (after the car warms up). But it still makes me wonder, why isn’t anything working and is there a cheaper solution than buying some anti-fog stuff on the net that GUARANTEES it will work. Any help is appreciated.
I used to have a cloth that was treated with some anti-fog solution, it worked fine.
BTW- another, faster, trick is to use your car’s A/C, especially in winter. Crank the A/C and freeze for a few minutes until your car engine warms up, and then switch over to heat. I worked in a car dealership and had to use this trick all the time when re-arranging the lot in the dead of winter. Waiting for the heat to come on took 5+ minutes, with the A/C it took a minute or two.
-Tcat
Just make sure your heating/cooling/ventilating system isn’t set on “recirculate,” instead of letting fresh air into the system. I know it’s counter-intuitive, but it seems that car windows fog up more easily if it’s set on “recirculate.”
In my experience, turning on the A/C is quicker than turning on the heat. I guess it’s just quicker to condensate the fog than to warm up the windshield. If you don’t have A/C, try opening your windows slightly - circulating cold outside air will have the same effect.
This site has a discussion on the physics of fogging (dew point, relative humidity) and offers advice.
I suspect the antifog coating are supposed to work by providing a very water loving surface. the water still condenses, but does so as a thin film (clear) rather than droplets that scatter light. I have no idea how good the stuff you buy for windows is though.
I thought I read here somewhere that if you have a defrost setting in the car it runs the air through the AC condensor anyways, so you don’t need to use the actual AC. If you don’t have AC at all then you’re screwed.
Backwards. Fog nucleation on windows occurs at hydrophillic sites such as hydroxyl groups on the surface of the glass. This site has a bit of discussion of the process. Anti-fog coatings are thus hydrophobic substances; either a grease, or an actual siliconizing agent that eliminates charges on the surface of the glass. The effect is to make water bead up rather than spread out.
This is true for some cars but not others.
I’ve also noticed on a lot of cars you don’t have to freeze. You can turn the AC on and the heat up (with the control set on defrost) and the window will clear right up.
Having a leaking windscreen, or heater matrix (if it’s in the car) can exacerbate the problem.
V
please don’t put other contributions down when you obviously know little about the subject. That site you quote is a rather general one about condensation in the atmosphere rather than on windows!
almost every anti-fog material I have seen uses hydrophilic materials. The action seems to also be one of absorbing the moisture
e.g. see http://www.mxl-industries.com/hydro.htm
http://www.sctech.com/news.html
http://www.phoenixnw.co.uk/news.html
it seems possible to also use hydrophobic materials ( http://europa.eu.int/comm/research/success/en/ind/0032e.html )but I have yet to find a product containing these alone, though there may be one.
Damn you, Bill Gates!
FTR, Rain-X and Fog-X are not the same product in different containers. Ask me how I know this. 
There’s no need to get snippy scm1001. Obviously you’re familiar with coatings I don’t know much about, and I’m familiar with technologies about which you know squat.
That leaves the answer to the question of antifog coatings somewhere in the middle.
First, just to show they exist, here’s a couple of hydrophobic anti-fog coatings:
for glasses, windshields etc..
siloxane (silicone) based coating, mostly for lenses.
A quick google will show you many more such coatings. They typically get used on camera lenses, and fancy optics, and most, but not all, tend to require careful treatment to avoid damage.
These hydrophobic coatings work by preventing water from ever finding a nucleation site on the glass, upon which to bead up and form fog. The hydrophilic coatings you described work by distributing moisture evenly over the surface of the glass; the water (fog) is still there, you just can’t see it.
So there are two ways to skin this cat. I happen to know more about the former, and you the latter. Your first post came off, to me, as wrong. With a little research, I stand corrected. As do you.
Peace.
You should use a Mac instead. We never get fogged! I can’t imagine why anyone would use a system that’s subject to fogging, what’s wrong with you people anyway? What? Oh…never mind!
[/Emily Litella]