These are an outstanding base layer. I live and work in the outdoors in the Pacific Northwest most of the year and find these to be an essential. You can probably find me wearing a mid-weight Smartwool top and bottom everyday for about seven to eight months each year. (I highly recommend stocking up on these.) A minimum of bulk and weight for backpacking, but an incredible value in warmth and comfort. The natural wool fabric is far superior in comfort, warmth, fire-safety and odor-control compared to the synthetic long underwear we used to wear. These are wonderful; I would recommend them in a second.