If you are after a good synthetic I would strongly recommend a (spun) polyester over polypropylene, simply because polyester is softer and not as scratchy. Unfortunately all the synthetics get pretty wiffy quickly - even those that say they don’t. Well that is my experience (also using MTBing, hiking, snowboarding etc)
I got a couple of the fine nit v neck base layers that I live in during winter… Wether it be cycling or going out out side in general.
It doesn’t wick as well but you don’t acutally notice this until you go to take it off and it’s damp…
Fact is you really don’t notice while your using the darn thing and that’s the key. Not only do the keep you warm when wet and don’t stink, they regulate body temp real well. If you find your self out in warmer conditions that you thought you were gona be in you don’t over heat so badly.
I got the rapha merino arm and leg Warmers this winter and they have been one of my favorite bits of winter kit
As for washing… It depends on the post ride condition… If its covered in salt stains you kinda Gota wash it.
If not you can sneak another ride or 2 outa it.
When I used to snowboard in japan a fair bit I would live in my ice braker merino base gear for 4-5 days at a time… including sleeping in the dam things…
The round the world yacht racing teams that used ice braker would go 40 days between washes…
Another plus one for Rapha merino base layers, wearing them everyday through this shite Melburn winter.
A few years ago I bought a capilene base layer from Paddy Pallin’s or Bogong on Little Bourke st and it was awesome for snowboarding in. It’s made by Patagonia comes is a few different ‘weights’. more info here