For those who have product, are the pants thin enough to wear under jeans and/or leggings? If between sizes, should I size up for use as a base layer?

I can wear mine under my jeans. I normally wear a L, and got these in a large. They are a little loose, and so if I bought these again, I would size down a size, as I like thermals snug. These are great looking, but also, run short. I am 5'8, 170lbs., and would order a M if ordered again. I will probably not order these again, as they run short for me, and did not do that good of a job keeping me warm in the 50's with wind out on the water in Galveston. But, they are super soft, super comfortable to hang out around the house inside. I would even put a tunic top on with them and wear them in public. I will look for something that is more like a true thermal for outside cold weather.

What is the inseam length?

Dear,different size thermal underwear has different inseam length. S:25.8 inch M:26.2 inch L: 26.6 inch XL:27 inch XXL: 27.4 inch.We hope our answers can help you.