Does anyone know where I can get rigid 100mm round ducting 90 degree connectors? I am really struggling to complete my kitchen extraction. It seems as though everyone does flat ducting these days but we had a very nice man from Expelair come round and do some working out and he based his maths on 100mm round ducting. I have tried contacting him again but I may have used up all my brownie points so am trying to do it myself. It is a long way to the nearest external wall 6.5 meters and as I understand it flexible reduces the air flow considerably more than rigid. To be inline with building regs F1 I need to achieve 30 l/s of extraction which is possible using the instruction the epxelair man gave us. I have a very strict bulding inspector to impress so I want to have done everything in my power to answer any further questions, I'd appreciate any advice on the subject.