I live in S. Calif. and bought these for chilly nights around 63 degrees.
My Mid-Weight Duofold were too warm, so I decided to try these. I'm very happy with my purchase, they are just perfect for a chilly night, yet not so warm to make me uncomfortable.

The shirt is also not bulky therefore these can be used to wear as underwear when weather is colder.

Being 5'7" 165 lbs 33 waist I chose Medium which made a perfect fit. Not too tight, not too loose. If you buy the pants of same: - The beauty of the pants are that the legs don't ride up while tossing and turning in bed.
Being 81% Poly 14% cotton and 5% Spandex gives this shirt a soft feeling yet will not shrink in the wash as 100% cotton does. They very are light weight and very comfortable.
Excellent product and highly recommended if you like quality.