I wash all of my Icebreaker merino wools on cold tap water, gentle cycle, set to low spin, hang air dry only. I wash about once every 8 weeks. I have not noticed any shrinking or destruction of the fabric.

Tip: be careful wearing your merino wool on public transit. If a bedbug decides to hitch a ride, how will you know? The only way to be safe is to wash it on hot and also throw it into the drier on high; thus ruining your wool. Your best bet is never to bring merino where nasty critters are likely to be found.