Hi all,
I don't want to come across as a filthy bugger however, with this post I may well give that impression  :-[
Anyway, personal hygiene matters aside, I'm afraid to say that as a result of urban/cavers myth, I was reliably informed* you should not wash undersuits too often....Which I don't. But, although I can put up with my own 'funk', I've noticed the polartec pile is now looking a bit thin. I feel that a decent wash may 'plump up' the fibres. This may also restore some of its thermal properties and thus de bunking the urban/cavers myth....not to mention increase my popularity with my caving companions.

So, my question is, what's the best stuff to wash undersuits in that may even restore fleece pile?
Cheers
'smelly' skippy
* The reliable source came from a CPC member, that many of the northern cavers may know but who wishes to remain anonymous.

I wash mine after most caving weekends, although on a cold wash with very little detergent and no fabric softener - it's holding up alright so far!

https://www.polartec.com/faq

Most Polartec? fabric can be washed in warm water and tumbled dry on low and in most cases this will deliver the best post-wash feel and performance.

However, every single Polartec? fabric can be machine-washed cold and line dried and a few of our fabrics require it. This approach is the most gentle for the fabric and is also the most energy-efficient. One of the greatest environmental impacts of our clothing is washing and drying over the life of the garment. Using cold water and line drying saves a large amount of energy. And most Polartec? fabrics are stain-resistant (requiring less laundering) and dry extremely quickly on their own.

The care instructions for the majority of our fabrics are: machine wash warm, tumble dry low, do not use bleach, avoid use of fabric softener, do not iron, and do not dry clean. Since we do not create and manufacture the clothing, we do not know what type of trim or other materials our customers are using which may affect care instructions. Always follow the care label instructions on the garment.

The addition of fabric softeners affects the function of the water repellent applied to some Polartec? fabrics but often diminishes the static problem. There are various brands of softeners with different chemistries and some will help static at the expense of water repellency, and others will have no effect on either. No softener will damage the basic fabric and will come off in the next wash. We do not recommend using fabric softeners on Polartec? Power Dry? or Polartec? Power Stretch? because it may inhibit wicking and drying properties.

I have always washed furry suits after every weekend's caving. My current Meander furry suit is 10+ years old and the fleece (made from Polartec Power Stretch) is  absolutely fine

Refer to https://www.polartec.com/faq  for more info.

I wash mine after every trip on a warm wash with minimal detergent. My previous one lasted about 350 trips before it became a little too thin.

Thanks folks..

....Its in the washer now 

I just put mine in the wash as normal (30 degrees, with laundry liquid) with any other clothes... Doesn't seem to have done it any harm really, it gets a bit less soft and fluffy after a while but on the whole it smells and feels much nicer to put back on...

It's much better to wash them frequently. They are better to move around in when clean, they are warmer when clean, they dry quicker when clean and they last longer. Mud wears fabric out a lot faster than washing does.