From http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15&page=4#Item_10 :
Insulation has a unique position, when considering its embodied energy/petrochemical content.
It's unique in that lighweightness is its essence, so in a way the less of the petrochemical stuff there is in it, the better it works. At any rate, accepting a relatively tiny amount of 'eco-nasty' petrochemical material as insulation can result in such enormously 'eco-virtuous' petrochemical in-use fuel savings, that the former is so vastly outweighed by the latter, that it's almost riduculous to insist on sheeps wool or something.
By all means, if sheeps wool etc does as well, then why not go for it - but on the whole the non-petrochemical alternatives
need greater thicknesses therefore more of other materials to create the necessary void space to fill
don't have fringe benefits like ease of ensuring no gaps, membranes/airtightness etc
cost more
are much more palaver generally.

Katymac said:
>Isn't Hi-tec expensive?<

Hi-tec can be ultra-cheap, when mass demand makes hi-tec robotised manufacture worthwhile; this phenomenon is well known in computer chips, computers as a whole and electronics in general - there seems no end to the freefall of their price:performance ratio.
In the past, materials (big quantities of), assembly (labour to be paid) and distribution dominated the price of goods. These costs were hard to reduce dramatically and still are, for traditional hardware, buildings etc; even for hi-tec engineered goods.
In a modern hi-tec (typically electronic) product, what you're buying is mainly the costs of design/R&D, marketing and distribution. Hardly at all material costs because so little is used, ever-reducing assembly costs because labour cost is replaced by the finance cost of buying sheds full of robots. That's when economies of scale and automation can really kick in.
Watch the same happen with PVs, which, being just big electronic components are ideally suited to the same.
Hi-tec isn't just electronics - it's anything where little material is used, and robotised production can be applied. E.g. insulation.