Recticel Instafit Polyurethane Insulation board (L)2.4m (W)1.2m (T)25mm

Most people use the R or U value, not the lambda. Why don't B&Q just make it easy for people?

As for this, you want a high R, so:

R = length (or thickness) / lambda
so R=0.025m / 0.022
= 1.13

So these Recticel insulation boards are actually fairly good, and exactly the same thermal conductivity of 0.022 W/mK for the Kingspan TP10 or Celotex. If you need a board immediately then fair enough pricing.

Feels warm just touching it, the heats bounces back. Super easy to score, snap and wedge into rafters and screw onto walls of our cabin which we hope will make it less hot in summer & warmer in winter to be a home office/ school. Still not finished as waiting on rest of my order but happy so far. Do beware of the metallic paper covering it though, I was solo DIY-ing and sliced my fingers on it, its like a razor.

This is not for cavity walls, see the manufacturers website

An equal replacement for Celotex and a fraction of the price. Also better for the environment, what’s not to like? Cuts with a simple hand saw.