303 High Tech Fabric Guard

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Properly applied it works! 303 Fabric Guard is primarily…

Rating: rated 5 of 5 stars
Source: bought it new
Price Paid: Depends on size.


Properly applied it works!


  • It works!

303 Fabric Guard is primarily used to waterproof Sunbrella fabrics and in the boating industry, Bimini Tops as well as convertible tops for automobiles. It's since made is way to the camping world.


It comes in a variety of sizes including spray and gallon size.

I've used 303 Fabric Guard on Bimini tops on numerous boats while in Florida. A single application lasts about a year properly applied.

I've used it on stuff sacks, backpacks, three tents including a North Face VE24 as a replacement for the old urethane coating it had. And I'm currently in the process of using it on the exposed sides of a Catoma EBNS Enhanced Bed Net System's rainfly and floor tub to supplement its urethane coating, which it has on the interior sides of the fabric.

303 Fabric Guard has placed first in tests of various waterproofing agents done by Boating industry magazines. The most recent test between six name brands in 2014.

303 Fabric Guard is a fluoropolymer based waterproofing agent. Starting out with a clean dry fabric and heat are essential to a long lasting waterproofing.


Wait for a clear sunny hot day with low humidity for best results on items that can't be put in a commercial dryer.

Clean fabric with a soap that leaves no residue.

Make sure it's fully dry and apply an even coat of 303.

Allow 8 hrs to cure in the sun.

Heat drying in a commercial dryer.

Once sprayed with 303 on a good sunny day, wait till it dries and order is gone (15 minutes to an hour). Then put the treated item in a commercial dryer at 115°-125°F for 2 hours or more to complete the curing. Usually this means either a low or medium heat setting depending on the dryer.

Allow another 6-8 hours once done to fully cure just to be on the safe side.

That's it, your done.

Application Tips:

Refrain from saturating the item when spraying. It's hard, I know, I've done it myself. But force yourself to spray a light coast and wait a few seconds. The material should darken.

Spray two light coats rather than one heavy coat. Wait till the first one is touch dry, then spray a light second coat in the opposing direction. i.e. if you sprayed left to right, next spray up and down.

Hang your tent or rainfly peak towards the ground when spraying. This way the heaviest coating will be at the peak where needed.

Drying tip:

If using a commercial dryer, I add in some dry fluffy large towels that I've washed previously in a non residue soap. This may or may not make any real difference but my thinking is that the cotton towels retain heat better than the synthetic material of the tent or rainfly etc, and help transfer that heat to the item I'm treating. As well as adds some cushion and bulk to the load. Remember, you're tumble drying your items for 2 or 3 hrs. I want to protect them and help the curing process along as much as possible.

You can use an oven to heat cure your item. I have heard of people doing this. And for the full 8hrs... If your oven can be set that low, it's worth a try for sure.

Cool weather application:

If you must apply in cool weather, not below 55°F / 70°F+ preferred, follow the method using a commercial dryer.

A hair dryer may also be used but use common sense when doing so.


IF your stuff sack, tent, rainfly, backpack, etc, etc, was made from a silicone impregnated fabric; or you sprayed it with a silicone based waterproofer in the past this or any other fluoropolymer based product may not work on that item. Some manufacturer's have stated fluoropolymer's will not bond properly to fabrics etc, that have previously treated with silicone based products.

I don't know this first hand as I've never used silicone based waterproofing on anything I own, or owned silnylon products.

Some manufacturer's say silicone based waterproofing will wash out but may take several washings, others say it won't completely wash out.

This is simply information I read from some manufacturer's data sheets and their recommendations as well as direct emails from them asking about this.

Just putting that out there so you can make a more educated decision.

Try it, if it works, great. If not, you know why.

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