Silnylon as VBL

Yes, of course you can use silnylon.

But a word of caution about making 'pygamas': make them very loose! I make my own 'liner pygamas' out of 8 mm silk. The first pair I made were modelled more on lycra ski clothing. One wrong movement in bed and they split right across my back! Get some pygama patterns and see how loose the patterns are.

Then report!

Cheers

Hope you don't mind if I jump on here with some questions.

I've been thinking about borrowing a friends sewing machine and trying this out with Silnylon or Cuben. Any thoughts on how you should set up wrists and ankle closures? I'm sure if the VB clothes are to be effective, you need a seal, otherwise moisture could escape into your insulation. I was thinking velcro tabs. How about around the neck? Zipper? Velcro? should you make some kind of VBL hood?

It's kinda relative, really. You don't really need an airtight seal… you're going to prevent 99% of the evaporative heat loss and moisture into the bag. Elastic at the wrist would work, or a velcro closure. If it were mine, I'd just sew a collar onto it kinda like most down vests have. Just don't make it huge, and it should seal well enough when you zip it closed.

Loose openings are nice if you want to vent, otherwise
wear them under a stretchy layer to keep the most vapor
right next to your skin.

No need for cuffs etc.

Wrist and ankles – don't make them too tight. 1 mm hat elastic isn't bad, but make the tubes large and carry spare elastic. Close, but not tight.

Neck opening – I think you may need a gusset here and a velcro tab across the neck. You should integrate the shirt with a hood, but it is worth wearing a very light soft hood under the VBL hood – and light thermals as well.

Cheers