Wookey

It is indeed very rigid. It's essentially like a piece of timber. I've just used my first bit under the front door, and am planning to use some more for the EWI windows as in this thread I've also just done the calculation comparing 100x75 compacfoam batten, 50x50 timber batten and 6 off 3mm thick stainless and galv brackets 80mm wide. This is fitting a U=0.92 PVC+ali frame into 160mm of pavatex woodfibre, so Wall U is 0.19. I used Therm for the sums (which is a very annoying piece of software!). Psi values: compacfoam: 0.008 W/mK timber : 0.014 galv bracket: 0.041 Stainless bracket 0.036 However as the brackets are only 11% of the length the average psi is: galv: 0.012 stainless: 0.011 So compacfoam is best, but metal brackets are fine too so long as the frames are well-lapped with insulation. Stainless brackets seem surprsignly expensive. Cost is £10.80 galv brackets (90x90x62) £ 46.44 Stainless brackets £ 28.90 1m compacfoam (6 x 166mm sections). So it's not really that expensive. It is if you line the whole window perimeter with it, but you might as well just fit the load-bearing blocks, then put EPS between them. You could use 1.5m with a 1m piece across the bottom and 4 blocks up the sides. That'd be £44.85. per window. This is the 'line all round the edge method by the suppliers: https://www.youtube.com/watch?v=5sSKsKB9doc This is the 'use blocks' method: https://www.youtube.com/watch?v=GUUrd7dbBzU