PIR vs Glass Mineral Wool insulation Performance

[farthings]

Hi apologies if this has been covered before but i've looked and can't seem to find an answer.

Can anybody give me an answer in laymans terms as to how much more efficient PIR insulation such as cellotex, Extratherm etc is when compared to standard mineral fibre?

i.e. for 300mm mineral fibre how much PIR (polyisocyanurate) insulation should I be looking at?

Many thanks
Ian

[welsh brickie]

it depends on the type your using,extratherm foil each side with foam 50mm thick is equal to 300mm of glassfibre.