Ripstop 1.1 oz VS Momentum 90 .9 oz

I cant comment on which is better. But I can tell you that the jacket with more insulation will be warmer. Infact if you made two identical insulated jackets, but the shell materials where different. I would think that the one made of 1.1 sylnylon would be warmer(less breathable). Even if its only 1.1 nylon(nonsyl) I would think it to be warmer based on the more breathable momentum properties. This is all hearsay on my part.

What is the purpose of your jacket? what conditions will you be using it in?

I wish i had used momentum on my projects. I have never heard any complaints about it at all, and it is lighter, a bit. If i was making all my stuff over i'd really try and get my hands on the momentum.

It's not silnylon, just plain 1.1 oz ripstop.

I want the jacket to be as versatile as possible, but mostly I will use this jacket under a quilt or a light sleeping bag in 20-40 F nights. (traditional thru-hiking season stuff).

I'd pay the extra money for momentum not because it's lighter, but because it looks better. The 1.1 oz ripstop from thru-hiker is very shiny on both sides, so that gear made of it would look a bit weird. (I've experience only with dark green fabrics, other colors may be different, but I don't think so.) Momentum looks and feels much better. Difference in weight is negligible, momentum might also be a bit more windproof and has better DWR.

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I agree that you should spend the extra money for the momentum. The momentum looks and feels better and is more water resistant as has been said. It's also lighter so the finished jacket might be a hair or two lighter than one made with 1.1oz ripstop but hardly noticeably so. I've used both momentum and 1.1 ripstop (for quilts) and really prefer the momentum.

I have used both 1.1 and Momentum in bivy sacks. I haven't noticed any difference in performance.

So from my perspective, the issues would be appearance v. cost. For a garmet, I would go with momentum for the appearance.