I came across this term on another thread. If I have got this right It relates to the 'warming effect' of natural wool when it becomes wet. This does ring true in that I can remember many fishing trips when I got an old wooly jumper wet and still felt warm.

My question is this, Do we think this is a further advantage in using this kind of natural insulation?

Very interesting - on googling (both sorbtion and sorption):

From http://www.greenbuildingstore.co.uk/ins-thermperf.php
Condensation Control
Wool generates heat when it absorbs moisture from the air. That energy is known as the 'heat of sorbtion' and account for the warmth felt by wearers of woollen clothes in winter conditions. When the air is saturated with water vapour, wool absorbs some 40% of its dry weight in moisture, producing 960 kilojoules of heat energy for every kilogram of dry wool. This warmth isn't noticeable inside the building but it acts to prevent condensation in construction cavities by maintaining the temperature above the dew point.

And this: http://www.merinoinnovation.com/awi/en/Home/about+merino/Proof/proof_warmth_en

So there's something here - or does it depend upon contact with the skin?

We live north of Auckland in New Zealand and breed Arapawa sheep and have numerous fleece awaiting some form of "project". This merino-type wool is very fine and has excellent insulating properties, but the staple is rather short. I would like to be able to make my own insulation for a renovation we are about to undertake - has anyone out there any ideas about this?

I think Biff is referring to Phase Change which occurs when a liquid is changed into gas and vice versa.

It is at this point that heat is either absorbed or given off.

I'm not too sure just how significant this heating and cooling effect is, but the other aspect is the humidity buffering effect. In humid weather the wool absorbs moisture and then releases it on a dry day, helping to keep steady conditions. I'm not quite sure why this is useful?

Thanks all for your responses. I must say I am still unsure as to whether this 'effect' is desirable or not. For a start, a vapour barrier on the warm side of the insulation will prevent such an effect from the inside conditions. Or is a vapour barrier not needed?

If it is than that just leaves the external environment and in order for moisture to be present [through condensation] there must be a reducing temperature gradient to the inside, yes?

Posted By: biffvernonThat's right - no need for a vapour barrier.

There must be caveats to that Biff - essential to have an outward gradient of vapour resistances if not using a vapour check. BuildDesk free U-value software also asseses condensation risk. Rule of thumb is inner layer's vapour resistance to be minimum 5x (some say only 3x) the outer layer's. E.g. ply/OSB inner sheathing and water-resist plasterboard outer sheathing or of course breather membrane achieves this.

Tom, there are millions of old buildings that don't have a vapour barrier in the walls. 'Breathable' is the trendy word for it.

Guest, come off it! We're talking happy organic sheep that have munched nothing but Lakeland fell fodder and come in a range of colours known as Herdwick Grey. (Chernobyl caesium is not volatile.)

OK, just spell that out, for those of us of little brain.

For example: 15 inch thick solid masonry wall.
Two posibilities:
1. on internal side of wall add studwork to support Thermafleece and clayboard and distemper.
or
2. on external side of wall add studwork to support Thermafleece and timber cladding.
No vapour barriers in either case.

What is the 'definitely big trouble risk'?

Why not check with the manufacturer of Thermafleece to see what applications they can suggest for the product? Their experience will indicate the type of roof/wall/floor/timber frame/acoustic systems the product has been used in and perhaps how resistance sequences can assist in reducing dewpoints and allow rapid drying systems to function. The critical feature with all constructions is not whether there is a condensation element but how quickly that can be dispersed.

I've found sheepswool to be a great product to work with and would certainly recommend it. It's worth looking at the options though and there are number out there with green options. I found www.burdensenvironmental.com to have a wide selection so worth a look in terms of checking out your options.