How Waterproof is Silnylon?

[LostInSpace]

What is waterproof?

I have a Sea to Summit “Ultra-Sil™ Dry Sack - 8 Liter.” I wanted to see how well the stuff sack would work as a temporary bucket / water carrier. I filled the stuff sack with water, and the hydrostatic pressure caused the water to ooze through the fabric. Although the water oozed slow enough to enable me to carry water in it, the stuff sack certainly is not waterproof in this situation. It is not even close to a 1000mm rating. See below.

1.Does anybody rate the water resistance in silnylon?
2.What test method is used to rate water resistance?
3.Has anyone seen, or does anyone have, the results of any tests?
4.How different are the silnylons among manufacturers?
5.If Sea to Summit can tape the seams on their stuff sacks, what prevents manufacturers of silnylon tarps and tents from doing taping seams?
6.Do tarp and tent manufacturers get water resistance test certifications from the fabric manufacturers? If not, why not? If so, why not publish the information?

According to the manufacturer, the stuff sack is “Made of Ultra-Sil™ nylon, a polyurethane coated Siliconized Cordura® for ultimate waterproofing and maximum durability. All seams are double stitched and tape sealed.” Published dimensions are 6.5” x 18”.

Manufacturers of polyurethane coated fabrics used in tents frequently specify water resistance in accordance with the American Association of Textile Chemists and Colorists (AATCC) Test Method 127. A sample of the fabric is clamped in place horizontally on the bottom of a glass, metered cylinder. Hydrostatic pressure is increased steadily by increasing the amount of water in the cylinder. The results are in the depth of the water in the cylinder, e.g., 1,000mm, 10,000mm, etc. The U.S. standard deems a material that resists anything above 1,000mm is waterproof. I think this is a Federal Trade Commission standard, but I am not sure. Note that 1,000 mm is 39 inches.

AATCC Test Method 127-1998 (Water Resistance: Hydrostatic Pressure Test)

This test method measures the resistance of a fabric to the penetration of water under hydrostatic pressure. It is applicable to all types of fabrics, including those treated with a water resistant or water repellent finish.

AATCC Test Method 35-2000 (Water Resistance: Rain Test)

This test method is applicable to any textile fabric, which may or may not have been given a water-resistant or water-repellent finish. It measures the resistance of fabrics to the penetration of water by impact, and thus can be used to predict the probable rain penetration resistance of fabrics. It is especially suitable for measuring the penetration resistance of garment fabrics. With the instrument, tests may be made at different intensities of water impact to give a complete picture of the penetration resistance of a single fabric or combination of fabrics.

AATCC Test Method 42-2000 (Water Resistance: Impact Penetration Test)

This test method is applicable to any textile fabric, which may or may not have been given a water-repellent finish. It measures the resistance of fabrics to the penetration of water by impact, and thus can be used to predict the probable resistance of fabrics to rain penetration resistance of garment fabrics.

[hammock engineer]

I think it is not a question on how waterproof the fabirc is, but is it doing what it is intended to?

A waterproof stuff sack is designed to keep the things inside from getting wet from outside sources. The weight and corresponding preasure from the water inside may have been enough to push some water though the material. I have seen nylon drybags (not used any yet). I know that REI carries them. I was debating buying one to use as a food bag.

Generoll posted a test he does to his tarps/tents that may help. Hang the bag with something inside (other than water). Then spray the bag with the hose. This will tell you if it keeps the water out instead of keeping the water in. You could also submerge it in water to test it.

Hope this helps.

[RockyTrail]

. I have seen nylon drybags (not used any yet). I know that REI carries them. I was debating buying one to use as a food bag.

I use a urethane-coated nylon "drybag" as a food bag and it's plenty waterproof for use as a bear bag. No need for fancy stuff, go to Wal-Mart and get a "laundry bag" in the camping section for about $5 , about the size of a small pillowcase. Put food in it, twist the top, then fold over the twisted top like a drybag. Then I hang it on a rope with a simple lark's head knot around the folded over top. Cheap, simple, works like a champ.

I like the sil-nylon, but the urethane coated stuff is a bit tougher in my opinion and better suited for rope and tree abrasions. Also it makes a nice "tablecloth" when spread on the ground for managing your food items when cooking.