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Thanks very much Nick. Heard about Origins's aerogel option / approach to improving thermal efficiency. When I last checked, they wanted a massive premium for the option, not quite sure how the pricing compares these days but worth looking at. Thanks again.

Thanks for the attached link of producers; more higher quality options in Europe than the UK.

Thanks Mike for your added insights. Very much appreciated. When manufacturers start caveating performance data with 'up to', it's generally a good idea to be finding the exit door. The lack of thermal / independent testing is another red flag. It's back alu/ wood options for me with more verified thermal performance tests.

@SBMS Did you end up going for the Senior PURe window system in the end? I find it rather impressive if the Uw claims are true as stated. My understanding is that the performance gain over Aluclad wood profiles is coming from using a polyurethane thermal break instead of polyamide. If one can achieve passivhaus sub 0.8 uw values with the Senior system, high sound reduction values and not have to worry about chunky wood profiles internal and having to paint them periodically, what's not to like?