Recently I made long underwear bottoms for both my kids. Two sets each, from the following fabrics:
Polartec Powerdry w/Xstatic. This is a t-shirt weight directional wicking fabric that weighs 3 ounces per square yard.
Polartec Powerstretch polyester/nylon blend. One side is fuzzy velour and the other side a smooth knit. Weight is 6 ounces per square yard and it’s much thicker and plusher than the Powerdry.
I wrote about the fabric and construction in this thread:
Polartec Source and my first garment sewing project.
Since then the kids have used their long johns for one hike/snowball fight and several fort building/snowball fight days. They used just the Powerdry, just the Powerstretch, and Powerstretch over Powerdry. This was under either nylon hiking pants or jeans. Snow play in above freezing temps ended up with the outer pants completely soaked.
Powerdry did a good job of keeping the kids comfortable when it was damp. The inside felt damp and the outside felt wet after taking them off. Powerdry is pretty thin and not too warm. Sitting or kneeling in wet snow was cold. Powerdry under nylon pants dried quickly.
Powerstretch is amazing! When my daughter came in from hours of snow play her outer pants were saturated. The knit outside of the Powerstretch was saturated. She took them off and I put my hand inside- I could not feel any dampness! Because it’s about 4x as thick as the Powerdry and not very compressible the Powerstretch kept knees and butt from getting too cold when sitting or crawling around in the snow.
My initial thought was to encourage always using the Powerdry as a base layer and putting the Powerstretch over when conditions warrant. I have changed
my mind and I would only suggest Powerdry when it isn’t cold enough to allow use of the warmer Powerstretch. I don’t think layering the two adds much. The Powerstretch has excellent 4 way stretch vs. mostly 2 way stretch on the Powerdry. Neither is wind resistant so they really need some sort of shell.
I think the Powerdry will be better for transitional temperatures from about freezing up to 60F where managing heat is just as important as warmth.

