I'm gonna be sewing an Epic top bivy in a week or so, and am vacillating
(sp?) about what fabric to use for the bottom. I've ordered 1.3 oz 2nds silnylon from Thru-hiker. Here's a few other options I'm considering:

1) 1st quality 1.3 oz silnylon.
2) 70 denier 1.9 oz silicone COATED (as opposed to impregnated), fabric from seattle fabrics.
3) 70 denier 1.9 oz polyurethane coated ripstop.

Any thoughts on the relative merits of these? I have a 1-week window of time and sewing machine access, so I want to avoid trial and error as much as possible. Thanks!

FYI: I believe Ron uses #2 for the standard floor option for the LS:

http://www.sixmoondesigns.com/shop/shopexd.asp?id=36

I've heard silnylon will leak if you put pressure on it (ie lay down on it) on wet ground. I would go with silicone coated nylon, but I'm not an expert.

Where did you get the epic fabric? Is it available in retail?

Thru-hiker.com

coated/impregnated
same thing (at least when it comes to fabric)

Thanks for that clarification, Dave. Do you think the 70 denier 1.9 oz silicone coated is significantly more waterproof and/or durable, as as fabric that will be laid on top of, than the 30 denier 1.3 oz silnylon? Didn't see the 70 denier silnylon in your recent post under "misting" Thanks!

I just got samples of some 1.9 oz. 70d ripstop with a .5 oz SILICONE coating on ONE SIDE. That is over
twice the coating thickness of the combined
coatings on standard 1.1 oz 30d silicone ripstop.

As expected it appears to hold back water at a higher pressure than than either 70d with a .5
oz per square yard URETHANE coating or the 30d
with a .2 oz SILICONE coating. It appears to approximate the 70d with a 1 oz urethane coating
which is used in most quality tents and bivy floors.

I think this would be a good fabric for stuffsacks,
packs, and tent/bivy floors when you need more
waterproofness under pressure, or need extra
abrasion resistance. It should be tougher and lighter than similar weight fabric with a URETHANE coat.

Now I have to decide if I can use a 600 yard case.
It is only available in royal blue. Any poster's
think this would sell?

Not sure about others, but I likely would've bought some.

FYI, here's the details on Seattle Fabric's "1.9 oz" sil-coated nylon:

"It is a 2/3 oz. coating and it is in addition to the 1.9 oz. fabric. The total weight is about 2.57 oz/ sq. yard and it is coated on just one side. We do carry a 1.3 oz silicone impregnated that is coated on both sides and the total weight is 1.3 oz./ square yard.
Thank you,'

After reading about Silnylon at MLD website I am confused.

http://www.mountainlaureldesigns.com/fabric.php

It clearly distinguishes silnylon (impregnated) from silicone coated nylon.

Can someone help me out here?

im about to use up the last of my 70D silnylon from the last time you carried it. Really awesome stuff, it's a very versatile fabric.
If you could find some, a 1.1 base nylon with a .4 or .5oz silicone coating would be awesome for applications where more waterproofness under pressure is desired, but weight is still paramount. I think it could do a great job replacing the 1.3 silnylon all together because of its increased waterproofness. It would be ideal for bivy bottoms, UL pack panels, no-mist tarps, stuff sacks and ground sheets.

BTW, Do you have any plans to carry any more of that 6' wide silnylon any time soon?

Another possibility ... This article at Jim Wood's Basecamp contains a suggestion for making std sylnylon tougher and more waterproof ... at a cost of about 0.75 oz per square yard (a bivy I made gained somewhat less than that applying the treatment to just one side, but I don't recall exactly how much less)

Although it’s not waterproof, the lighter stuff is fine and I recommend it. This is because you should never be pitching in a situation where you are in a pool of water. All my shelters use 1.3oz and this has never been an issue.

Jim’s article is fine but it refers to waterproofness in the context of a pack pushing into your skin with some pressure when its very wet. In this case, I can personally vouch that 1.3oz is not water proof enough.