Pertex & Pile?

I use the Buffalo Special 6 shirt a lot. It’s good in the winter and I use it Oct to May. Pluses are warm and damp resistance except in heavy rain then you need to put a shell over it. It’s got great ventilation which is needed as you get hot. I live in the UK so our winters are mild. If its cold or damp the fibre pile garments work great and means I have to carry less spare clothing which equals a weight saving. But in the UK it also gets mild quick and on a weeks hike it often ends up to warm to wear at some point, and so goes in the pack. At this point you regret not having a spare light fleece to wear instead which means I tend to take one anyway and the weight saving is lost. Saying that the Special 6 makes a good warm top to wear in camp, but is bulky and takes up a lot of space in your pack.

I too have a Buffalo Special 6 and it's a fantastic garment for winter. I've been using it at about zero C, 32f, down to about 20f. But I do run very hot.

The teclite (lighter weight) or a Rab vapor rise or the like will be my next purchase.

I would say you'd almost certainly save weight below freezing, but any warmer then it becomes somewhat tricky to use as you'd need to be carrying something to replace it with, so you'd have to carry alternative layers anyway.

I also tend to wear it with a wicking layer beneath, just because those vents let your skin get cold at 20 degrees. (having said that most 'normal people won't need to open vents at that temperature).

As regards to the rain I've always worked on the concept that Pertex and Pile retains most of it's warmth when wet, and I've found that to be true – but I've been fairly lucky with conditions. If you're ok getting a little damp but remaining warm then it's ideal.

Snugpac seems to be the available version in the us.