Silk or Wool Long Johns?

I'm looking for long johns for worst case scenario that we need to move in the middle of winter. Also, if we bug in (and we've got no heat), we've got to be as warm as can be.

I've heard of silk long johns from the other thread, and while googling for it I also came across Micrawool. Check out the features:

Micrawool Long Underwear Bottoms - 70 Percent Merino Wool - Forest City Surplus Canada - discount prices

Is this better than silk? For trekking out - at least it's also good when wet. Your take pls.