The wall is in a 45 year old house that has standard UK cavity walls (red-brick on the outside, cavity, concrete blocks on the inside). Kooltherm K118 Insulated Plasterboard is what I'm thinking about.
Kingspan building regulation's page shows a target W/m²·K figure for the wall type. I'm in Scotland and for an existing heated home, 0.30 W/m²·K applies.
On the the product page it says:
As part of our Kooltherm 100 range, it provides a level of performance that is unrivaled in the world of rigid thermoset insulation materials with a thermal conductivity of just 0.018 W/mK across all thicknesses.
So (help me here) 0.018 is a lot less than 0.30, and it says "any thickness", so I could choose their thinnest sheets: 32.5mm and still be compliant with the regulations, right?
Maybe I'm getting lost in W/mK vs W/m²K..