Tent fabric

I too would like some guidance on this. I am near to a decsion to order a tent and the manufacturer wants to know. I don't know the difference and without some further infomation don't know how to respond.

If you are building your own, silicone impregnated fabrics (which means both sides) have better strength to weight as the silicone actually makes the fabric stronger. Urethane coatings for some reason weaken fabric strength, requiring a heavier base weight fabric to achieve a given strength. Manufacturers prefer a urethane side so they can heat seal seams with seam tape, which doesn't exist for silicone.

For the do it yourselfer, sealing with a liquid sealant anyway, there is no drawback to all silicone. Silicone does get staticy and attract dust more than polyurethane. Polyurethane at some point late in it's life gets sticky and stinky. I've retired more gear to coating reversion than I have to actual wear-out.

I hope this helps. One other thing, urethanes absorb more moisture than silicone, so a urethane coated tent that has exposed coating on the exterior will pick up a few more ounces pack weight when wet even if it appears dry or the beaded water is shaken off or mopped up. Urethane coated tents also are more prone to mildew growth when improperly handled for this reason.

Beats me, but I figure the folks at Hilleberg know their fabrics. Here's an excerpt from Hilleberg's 2006-7 catalog:

The Importance of Tear Strength

Greater strength equals greater safety. It is that simple. The stronger the fabric on your outer tent, the less likely it is to tear because of bad weather, rough handling, or inadvertent mistakes.

In 1975, a fabric supplier sent Bo Hilleberg a sample of a new fabric that was lighter and more waterproof than other available materials. When Bo made a cut in the fabric and tried to tear it, he couldn't do it. The fabric, the supplier told Bo, was coated with silicone, rather than the usual polyurethane. The new fabric was indeed very light and totally waterproof, but it was also incredibly strong. It was exactly what Bo had been looking for, and with that, our Kerlon fabrics were born.

All silicone-coated fabrics are not created equal. Our Kerlon fabrics are coated on both sides, with a total of three layers of 100 percent silicone. Certainly they are completely waterproof and very light, but our process also imparts a strength to the base material that is an order of magnitude greater than is possible with the more common polyurethane coating process. Perhaps more importantly, our coated Kerlon fabrics are far, far stronger than so-called "siliconized" materials, which typically employ a coating mixture of silicone and other coatings."

What I get is that double coating with 100% silicone allows for the use of lighter weight nylon fabric — or conversely, with traditional PU coating, a heavier weight nylon would be required to achieve the same tear strength.

Perhaps it is silicone coating that allows nylon as light as 1.1oz per sq. yd. to be used as tent material for 3-season camping?

Thanks guys. I was aware of all of the above, I am just trying to find out if there is more to it.
It is rather peculiar that as pointed out by Neil a PU coating weakens the tear strength of fabric whilst silicon will strengthen it. The main reason is that silicon impregnates the fabric rather then just coating it. I was hoping that someone would think of an advantage, apart from the tape sealing issue, of PU. I am thinking about reducing misting by using PU as the inside layer (?)
Franco

The type of nylon has a bearing too. Nylon used for life
support is type 66 which has higher strength. Genuine
parachute cloth is such nylon.

Thanks to all of you for the collective explanation of the issues here. You have corrected some erroneous assumptions.

Another reason companies use a sil face/PU back coating is to comply with government fire retardancy standards. The FR treatment is applied along with the PU coating. If it weren't for this need, you would probably see a sil only from more manufacturers.