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Insulation Values and Weights of Long Underwear

I was thinking of upgrading my long underwear (uppers and lowers) to something lighter but still very warm. I am 63 so have switched over to ultra light backpacking more or less. I usually take them backpacking in the high sierra more as an extra safety measure in case I get caught in some cold weather near the end of summer when it might dip down to below freezing. My current long underwear is old REI brand, 92% Polyestra and 8% Lycra. The uppers weight 9.5 oz and lowers 8.4 oz. I went to look at silk underwear, as I understand they are very light and very warm, on the website but it does not provide for weights. Can you provide some data on the various types in regards to insulation value and weights. I am a medium. 

Thank you, 


14 Replies

I've had success with merino wool from Smartwool, their 150 weight stuff.  I currently have a long sleeve crew neck shirt and some thermal pants, and a pair of their boxers.  I usually wear that when I sleep, and it works well.

Do you know the weight of your thermal shirt and pants? What size are they?



I'm a big guy, so I wear size Smartwool XXL.  My merino wool long sleeve shirt is 7.6oz, and my merino wool pants is 7.3 oz


Those are pretty light! Lighter than my older REI polyester base layers which aren't as warm. 



Hey, I would recommend the Krios Pullover ( and the Krios Long John ( by Beyond Clothing. I have both of them and they are my go to base layer whenever I'm going to be outside for an extended time in the cold weather. I usually put a shirt under the pullover though, just as an added layer. They are both very comfortable, I like the Polartec grid fleece material they are made of. Both products are Made in the USA too!

Also, today they are having a sale for a lightweight base layer shirt ( and pants ( I have the shirt in grey and I love it! Very comfortable, I have been wearing it as an everyday shirt. Both are imported.