Oh they are fab.
I knitted my own [and smug emoticon]
Wool is a natural fibre which, when its got its natural oil on, is waterproof, breathable, and self cleaning. Hence you never see wet sheep with their hair all flat hanging down around them. The water can't soak into it as the sheep produces its own lanolin like we produce sebum from our hair follicles.
The wraps I made were from untreated wool, still contained all its natural lanolin. So I knitted wraps and bunged em on baby. If however you buy wraps made of wool material or factory knitted, the lanolin has been removed during the manufacturing process by washing/dying etc and so you need to soak the wrap in lanolin (nappy suppliers sell it or Boots) to re-lanolise.
The breathability of the wool makes the baby more comfortable, the lanolin stops the wee soaking into the wool, and the self cleaning of the lanolin means that the wraps don't smell of the wee.
After a while of exposure to human wee though (as opposed to rain and a bit of mud in the field , the wrap will start to smell a bit and you know it needs re-lanolising. So you wash it very gently then make up a bucket of lanolin rinse (instructions on can of lanolin) and soak the wrap for ages, then hang up to drip dry and you are ready to go again for a few weeks.
I recommend wool for night or round the house but not under clothes/trousers as the wee will squash through the wool if a child is sitting on it or trousers are squashed against it.
Bet loads of xposts while I typed this!!