Here is the wording from the official list, in capitals, which you must all sign before starting. The trend of wearing a Tee shirt over the base layer may help your street cred but is NOT allowed. To ensure that your garments are warm when wet all your warm layers must be NON cotton. Wool is acceptable, of course, sheep keep on surviving but its very heavy and therefore its your choice.
Polyester gives the best warmth weight ratio and lowest water absorption.
Neither are polyester trekking type pants which are commonly worn on the assumption they are not jeans and therefore allowable. It is important to realise that exposure can occur even in sunshine, which means it will be unexpected and not easily spotted. You should keep an eye on your partner particularly when your blood sugar levels are getting low. If exposure strikes at that point it s critically dangerous. It is assumed by the organisers that anyone NOT reaching the overnight camp will be camped in safety elsewhere.