Long underwear question that is.

I am planning an Elk hunting trip to Colorado this November. In looking at my current list of gear I decided to buy some new long underwear.

I am looking at getting a few sets of Merino wool long underwear.

The question is should I get the 100% Merino wool variety or something along the lines of 80% Merino wool 15% Polyester 5% Lyrca???

Does anyone have first hand knowledge of the pros and cons of each???

Thank you in advance.

Regards,
Steve