Polartec invented this material quite some time ago. it cam in 50/100/150 weights.
This was the gradient to measure the temp or heat retention. those grades have since gone away. But every major manufacturer from Arc'teryx to Obermeyer has a top an bottom in the "150" wight power stretch. Recently loaned out my ten year old bottoms, that were still like new and have yet to have them returned. Oh well. I have since purchased a pair of Marmot and they work everybit as well. the only difference I see between any manufacturer is stitching patterns. all same material. they are bomber for everything . I run, hike ... climb... anything in the cold. wonderful for games too. I would however recommend using a residue free washer soap. or they get much more steamy as a result of blocked evaporation pores. the new win detergent from the Olympics is working fine. NO noticeable improvement over g-wash, nik-wax or pengiun.
I have worn this suit top and bottom in northern Wisconsin in snow storms while out running on Lake superior and was plenty warm.
I hope this helps.

i talked to BC.com, to marmot, to make sure these where what i was looking for. Clearly no one i spoke with had intimate knowledge of the product. These are just basic medium to heavy weight fleece pants. Who would recommend that for high aerobic activity, i.e. running, climbing, skiing? Not me.
Unless you're just looking for something to sit around in or sleep in look for something else. I've gone "for a morning jog" in -20 temps and wouldn't wear something this heavy... but perhaps that is a personal preference.

these will be returned shortly.

These are unique and extremely comfortable athletic pants, more comfortable than tights and warmer.
A couple of things. I'd wash them by hand. The waist band, which is fleece, twisted up on me. I just folded it down and they're fine. Sizing. They run slightly large. I am 6-1 165 and the large are a little big. The pants shrink a little in the wash but stretch back out.
To tell you the truth, I'm still not sure about these pants. All I know is they're better than tights or sweats because they're so light and comfortable.

Once I finally received the package, I tried them on to make sure they would fit. I was very impressed with how fleecey they where on the inside. They are so comfortable and warm, I didn't want to take them off. I found I was warm enough with out any pants over top. They are great lounge pants. Love the stiching as well, great design.

These turned out to be better than I expected. They are so soft inside and warm too. I finally found a pair of fleece pants that I like and are comfortable in. I recommend these for any guy looking to keep warm while outside in the cold, whether they are used as under layer or alone (of course depending on the weather). I love these enough to wear as lounge pants in my cold house :-).