There are reports of problems with synthetic underlayers melting to the
skin of the troops in bombings etc. They might well want to go back to the
wool now that they have itchless, machine wash versions. The superlight
stuff works better than synthetic too for wicking and staying warm when
wet.

Here are some example for research.
http://www.icebreaker.com/site/home.html
https://www.smartwool.com/default.cfm