I agree with all the above...Silk liners make a real difference on the comfort side of things, and a fleece liner is often all I use with my bivi bag. I once tried a cheap polyester liner, and found it to be a nightmare. It got damp quick, and stayed damp. Liners are one of the items where quality does count. Find a good stockist, and check them out the same way you would a bag.
Before critisising another, first walk a mile in thier shoe's...Then if they take exception, your a mile away, and they can't chase you.