I know it sounds weird but if you spit on them it seems to help but only long enough to burn a rod and then you are back at spitting on your glasses. Hey it is free but seriously not much helps the fog. But I have found that spit helps the best also if you exhale out of your mouth and direct your breath out of your hood that will help as well. Have you tried installing some cheater lens in your hood?Good luck man.

P.S. don't forget to take out your dip or else you will need to get some windshield wipers to clean your glasses. Have a good one.

some little wipes called sight savers work good i find.

Try this: take a small drop of dishwashing detergent (Dawn, etc.) and smear it all over both sides of the lenses, and them wipe them off and polish with a clean cloth.  I know it sounds wierd, but it seems to work for me.  If you can find a soap that is cocanut oil-based, that works well, too.  Something about that oiliness won't let the moisture fog up the glass.

I have known some old pipeliners that have glued a patch of felt fabric infront of their mouth/nose on their pancakes to catch the mosture from their breathe.

I think the best and cheapest thing I’ve found is a mixture of 3-parts water, 1-part white vinegar. Spray it on all your lenses, (both sides) and wipe dry.
Another trick is to get the inside of your hood / shield warmer than your head. I use a heat gun to warm my eyeglasses and the inside of my hood. I know in the field that could be a problem.

Fog-X,  made by Rain-X.

Griff

welder hood defog fan - defog fan for pancake hood Member Swap & Sale - Pipeliners Local 798

Seen this thought it might help.

The trick here is surface tension.  Any substance that lowers the surface tension of water, will reduce the ability of moisture to accumulate on a given surface. common hand soaps etc will do this, so does spit. another agents like water wetter, some types of anti freeze and brake fluid will do those ( don't think you would want them in your hood though :) ) 

With that in mind I used bar soap/hand soap by applying some and buffing it off, or I used spit when I was desperate.  When I was motorcycling in cold weather a bandana over the bridge of the nose would deflect all the breath downwards and they made helmets with breath guards.  Never seen a dedicated one for welding tho...

the various anti-fogging substances work to varying degrees of success but there's nothing special about them outside of being formulated to stick to glass.

ive helped a couple of guys areond here and the basic trick most of them use is their torch  wave it accross the inside of your pancake  i guess raising the temperature inside the hood keeps the moisture from building up  whatever the case it works  dont see why the same wouldnt aply to your glasses  good luck