Silicone Water Guard by Sno-Seal is one of the best spray-on waterproofing products. I have used it on tents, clothing, and boots.
I’m not a fan of spray-on silicone waterproofing, but sometimes it’s the only thing that will do the trick. For example, if you need to waterproof a nylon tent, it’s really the only sensible option. If you still have an old canvas tent there are some other, very messy, options, but spraying is so much easier that you might opt for it anyway. Also, to refresh the waterproofing on a winter coat, or a nylon shell, it’s hard to beat.
To use it on fabric, work OUTSIDE, on a very calm day. Although this product (unlike some others) does not contain flammable hydrocarbons, it really fills the inside air. Take it outside. Shake well, and try to spray evenly, although I find that I always get streaks with too much coverage. If this happens, hold the can farther away, but if there is any breeze at all this will make it difficult to get the product on the item you are spraying. In any case, let the silicone sink into the fabric and dry. Once it is dry and has had a couple of days to “cure, ” the odor will not be bad.
I have good results with it on nylon tents. It will keep you dry inside through several hard rainstorms and a lot of foldings and unfoldings of the fabric.
My results on clothing is mixed. It will help a garment that is already water-resistant be more so. But to just spray a nylon jacket and expect it to be waterproof is a stretch. It will be good for one good heavy soaking, and then you’ll have to re-spray.
Using it on boots is another matter. I prefer rub-on oil based waterproofing for boots, but if you have suede or fabric boots, you will have to use either a liquid wax, or spray. Once you make a choice which to use, you shouldn’t switch, because you won’t get good results with either one then.
Spray clean, dry boots thoroughly, and let them dry completely. Then when you walk through one wet field you might come home with dry feet. You won’t make it through two wet walks. Spray just doesn’t hold up on boots.
I have tried several brands of silicone spray and this one by Sno-Seal is the best, but their ability to last over time is limited.