They used ISO super 9 style foil/fleece insulation in a loft conversion
on DIY SOS last week.

Although sceptical for the same reasons, there are some genuine reasons why
it might be superior. The main one is that celotex leaves uneven gaps where
it is wedged between rafters, leading to draughts within the insulation
which reduces its actual effectiveness. Tri-iso Super 9 is rolled on in a
single sheet, so there can be no gaps for draughts to develop.

I'll know if the stuff works properly soon. My not yet finished loft
conversion has it. I will say that in February, the room became the warmest
in the house, despite not having installed the heating in it and having
hardboard for one window and roofing felt for another. Previously, the roof
had about 25mm of expanded polystyrene behind hardboard and was slightly
cold, but not excessively so.

There is a new version out called Tri-iso Super 10. This has been
independently tested to confirm that it provides the equivalent of 210mm of
glass fibre wool in actual installed conditions. I don't know if similar
testing was carried out on the Super 9, but they claim 200mm equivalence. It
has a similar construction, but the Super 9 is nominally 25mm thick, rather
than the 30mm of Super 10.

Christian.