In article , Lobster
writes
Bedouin wrote:
What's the best thin insulation available?

I was trying to spec some thin insulation recently and a structural
engineer mentioned something called "Tri-Iso Super 9", about which I
know nothing other than it's pretty expensive, so I didn't go any
further - others here may know something about it?

It's ****, avoid.

Sorry, to elaborate:
It relies on being fitted precisely in the middle of two 1" closed air pockets
in order to work; it is thin material but not an insulating medium for use in
limited spaces. It works mainly by limiting heat transfer by radiation but
then claims to "seal roofs against wind and damp, whilst retaining
ventilation" without mentioning that where the outer pocket is ventilated the
product will perform less effectively since heat will be lost by convection
instead of radiation.

Maybe have a read between the lines in the brochu
http://www.kensaengineering.com/pdf/79.pdf (209k pdf)

IMO, avoid foil based insulation systems, other types (foam based, celotex
etc) are more likely to achieve the claimed insulation performance over the
life of the property.
--
fred