I typically bring a pair of long underwear bottoms for 3-season hiking. They provide needed warmth for sleeping when layered under nylon hiking pants and as something to sleep in if my hiking pants get wet from rain. However, today I weighed them and discovered they are exactly the same weight (8.5 oz) as some fleece pants.

My question: Is fleece warmer than semi-tight long underwear bottoms when worn as a base layer?

The long underwear are Hot Chilly's Expedition weight, dense, and have some obvious spandex quality to them. The fleece pants are very similar to these (http://www.champaignsurplus.com/rugged_outdoor/military-fleece-pant.html?gclid=CLrS9I_mg7QCFeGDQgodCHwATQ.

I had a similar revelation last winter when I made some powerstretch tights and found them to be an ounce lighter than my Cap 2 bottoms. They're quite a bit warmer and are great on their own in cold weather. Except in warm weather, I take the PS tights.