Hi Bill, what you wrote is italicized and my comments are not:
“The outer layer: Are you hoping that the very-thin silicone mix will coat the fibers while allowing spaces for moist air to pass through? Like a DIY-EPIC sort of thing? Making your own, better, DWR?”
Correct, but some minor differences as compared to EPIC though. First, a different application process, and two, shooting for greater breathablity. EPIC fabrics typically were meant to be used in a single layer type application and thus tended to be highly water resistant with the resulting pretty low air porosity, though it varied from fabric to fabric. The one that I had bought, had quite low air porosity and wasn’t suitable for my purposes.
“Where DO you get suitably lightweight untreated polyester? Most technical sources seem to have factory DWR applied.”
Correct, that is one of the challenges, to find a suitably light but strong and well woven polyester fabric that doesn’t have a DWR already applied.
“Why must it be untreated? Is that for the silicone to stick better?”
It has to have no DWR treatment so that the silicone can adhere at all. For example, one time I bought some polyester fabric from DIY Gear thinking it would be excellent to apply silicone for my diy WPB experiments. The description mentioned nothing about it having a DWR treatment. I coated it with silicone, and ended up sending a sample to Richard Nisely to have it tested for hydrostatic head and air porosity. To my surprise (and a bit egg on face), the fabric already had a high quality DWR treatment and the silicone just came right off. Both chemistries are very low surface energy (factory DWR’s more so), but non compatible with each other as far as adhesion. Silicone is not quite as good as some factory DWR’s (especially the old ones) in the sense that it is not also olephobic. Thus why I mentioned that very occasionally a hot wash with a strong degreaser would be neeed to refresh a silicone coated fabric. But better than a factory DWR in the sense that it is a much, much thicker coating and thus far more truly “durable”.
“The middle layer: What do you envision for non-woven polypropylene? When you say to get it from Jo-Ann, are you thinking of something like this 1.1 OSY interfacing fabric? Do you really think that will breathe much?”
No, that is not the correct type of fabric. As far as non woven polypropylene, have you ever seen those reusable grocery bags made out of the soft and breathable material? These are typically made out of non woven polypropylene, and are usually quite breathable. I would guesstimate the average air porosity to easily be around 50 to 80 CFM range. You can fairly easily suck and blow air through the ones I’ve bought.
When I was talking about Joann’s, I was talking about sourcing an alternative to the outer fabric of silicone coated polyester-that alternative being outdoor woven polypropylene fabric.
“The inner layer: Monolite or Cloud — Is this mostly for comfort? To keep the polypropylene off of your skin? Or is it necessary to protect the polypropylene layer? Can we buy anything resembling Brynje’s coarse polypropylene mesh?”
As mentioned earlier, mostly to protect the inner, more fragile layer of non woven polypropylene from abrasion and body and/or plant oils (and as an extra layer for the thread). A more open mesh fabric wouldn’t help as much as far as the latter, and might actually induce abrasion through rubbing? I’m not sure.
“Outdoor woven PP mesh: Would that be something like this 1.2 OSY spun-bond PP landscape fabric? Is anything lighter available? I found lots of 3-6 OSY landscape fabric, as you said.”
The outdoor woven PP fabric is not mesh at all, but a sturdy, somewhat thick fabric like this:
https://www.joann.com/p/solartex-outdoor-fabric-dark-blue-solid/16977217.html
It is usually sold for outdoor cushions/furniture, shading fabric, and the like. I proposed it would make a decent, but heavy alternative for the outer of a front poncho insert. In my case, I have a rather short torso and so I would only need a piece of fabric that was like 1 ft x 1.5 ft, as an insert right over my chest area, and the rest of the poncho would be made out of UL silpoly or the like (shoulders, back, and lowest front part).
“It seems as though all three layers would total 2.5 OSY or more. Are you concerned about total weight and possible warmth of the finished poncho?”
Yeah, ideally one would use an UL polyester fabric to cut down weight, but as mentioned it is hard to find these without a DWR already applied. Many WPB fabrics are 2.5 or 3 layers already, but they are usually laminated which yes, does make them less thermally insulating. However, their lack of air porosity counter balances that. The greater the convection of air, the less insulation. As far as the weight, to cut down on the weight, as mentioned, I could get by with an insert as small as 1 ft x 1.5 ft on the front of the poncho. Obviously someone with a very long and/or wide torso would need a larger insert. But even then, if all the rest of the material is an UL silpoly, then it really shouldn’t weigh too much.
Btw, something like this would make a decent inner/center fabric for the non-woven polypropylene:
https://www.amazon.com/House2Home-Polypropylene-Interfacing-Stabilizer-Embroidery/dp/B08Q2FNJTP/ref=sr_1_5?crid=KBV0XO3TUB0W&dib=eyJ2IjoiMSJ9.2VYorcPCI13cS4ONUCk55frFKCfmQ3Wvo2VerXir89kYCnQwbtgPFJW7etzvvUrYQy8-6_FCkYvCOMmIkqCsS_D70PLPHI-VXvz2f6S9cRTwHnGAuLBXNbGgEBQ9CZMhHOjzEiVGsCL6my74xi4TpNdAjGYYhGuWtJWrkdEdk-me_8w4Ow463XBgU8aq4xTY1Qb8zlVWHwcvxaxFe2mQDaD8NETf5XFJsONHsI_mijqHpxCa5ljNEo5OMX3EzZmaEU3H7rG0Ja-q59uRAG0V8OC6rihvFzj9AWVHIpbnz5U.8yzWUzuVXnHf6xK0AAMfV7qmILyf_sJ5gduGbgknHxQ&dib_tag=se&keywords=lightweight%2Bnon%2Bwoven%2Bpolypropylene%2Bfabric&qid=1732320215&sprefix=lightweight%2Bnon%2Bwoven%2Bpolypropylene%2Bfabric%2Caps%2C379&sr=8-5&th=1
“I’m looking forward to hearing how this works out for you. It’s an interesting experiment!”
Thanks. I wish I had the time and energy to do more experimentation and creating. Ironically, I finally have the money, but as I’m working 3 jobs, one of which is a full time job, I just don’t have much time and energy of late. These projects will have to wait until Christmas break.
My first iteration (the needle punctured, low HH silnylon + 1443R Tyvek fabric was decent), but I strongly suspect it can be made significantly more air porous and still work.
Anyways, since this thread is about baselayers, I’m probably going to not talk too much more, if at all, about rain gear type systems here.
Cheers