How and Why Wool Nappy Covers work

So many people ask this, so I thought I'd post this explanation.

Wool is absorbent, but absorbs very slowly. Because of the body heat of your baby, and the warmth of the wool, it also evaporates, and this happens at the same rate as it absorbs. When evaporation takes place, the wet is turned into gasses. Most people think this will be steam, but in fact it's not. Steam is created when evaporated water condenses again, and this happens when the air containing the evaporated gasses, has enough wet in it to saturate the air. (This is called the dew point) When this saturated air meets something cooler, it will turn into steam and condense.

If you have a PUL wrap, the inside of the PUL will not let the wet get any further, so the amount of evaporated gasses builds up, and the air inside the PUL becomes saturated, and reaches dew point. Because PUL has a cold feel, the saturated air will cause wet to condense again, and get absorbed back into the nappy. This doesn't happen with wool, because it is warm, and can breath, so "dew point" is never reached, and the gasses continue one their journey, unrestricted by the wool, baby clothes, bedding etc. It will finally condense possiby when it hits the window of your baby's room in winter, but basically the amount of wet in the air never gets high enough to cause a dew point.

And that is basically why wool nappy covers work, and nothing gets wet outside the wool.

Gosh, reading that it sounds a bit scientific, but that's how it works anyway.

that is great as my mum keeps saying that i can't put bean in wool as it crawl and bean will over heat i can now show her this and it might help her understand a bit better

Well, I've learned something today

Whenever we've put anything cotton over wool it's always got wet for us. The only thing that hasn't is fleece.Not sure why that is but it's happened to pyjamas and sleepings so we ended up avoiding them.

We've never had any problems with cotton ect over wool it does feel cool but not wet for us. It's funny how different they all are.
Thank you the explanation. It took me two reads to "get it"

Whenever we've put anything cotton over wool it's always got wet for us. The only thing that hasn't is fleece.Not sure why that is but it's happened to pyjamas and sleepings so we ended up avoiding them.

Did you use hand wash only wool, was it lanolised, and was the nappy underneath absorbent enough? Also was the cotton over the top tight against the wool? If so, you would have got a squeezing effect. You need to make sure that top clothing is loose.

I just want to add to this. If you use wool with a sleeping bag, you need to either use a large sleeping bag, or leave it open a little bit. Otherwise the wool will breathe, but the sleeping bag won't!

Thanks

bump for Steph77