silnylon rain gear

My silnylon poncho seems well ventilated enough. I made a Parcho this summer – http://www.questoutfitters.com/10JuneParChoSewRedFileSz%20%281%29.pdf – but have not yet had it out in the rain. I think some people do use jackets of silnylon, but it's hard to imagine them not being clammy. I also made a pair of pants, and they do get a bit clammy. They may get turned into chaps, which might ventilate better.

I haven't used sil nylon rain gear, but I have used cheap non breathable rain gear.
If you are heading out into heavy rain the dwr on a wpb jacket will probably wet out anyways, so sil nylon jacket would work just as well while limiting the wear on your more expensive jackets. For the occasional shower or if you want to use your rain jacket for wind, yeah it's going to be super clammy.

"For those who use rain gear of any shape made of silnylon, does it get REALLY clammy after prolonged use or can vents keep it comfortable? Thanks."

Just like wearing a tailored garbage bag :)

You want all the vents you can get, regardless of the type of fabric used. Silnylon works for a poncho— plenty of venting there and it is over your pack, so really only in close contact in front. I wouldn't bother with a jacket. Get a DriDucks instead.

I've tried vinyl poncho

If it's windy it doesn't work so good, blows all over the place

I made up a jacket and chaps using 1.3oz silnylon. Jacket -full zip, hood, pit zips etc, at 7oz for the pair and very little volume they are nice to take along on any hike. The chaps work well and do not get too hot because of the top being open. Jacket covers top of pants area draining onto the legs portion. The jacket also works well but only if you wear something long sleeve with it. IE; if you wear a short sleeve shirt your arm sweat will cause the jackets sleeves to stick to you and can cause you to chill as it will conduct heat from you.
Being from the NW where the rains are typically cool I wear a light weight (170gr/m) merino wool long sleeve shirt under my rain jacket and use the zips to regulate temps.
[Dale