I know its very rude of me but I have lost the contact details of the lady who so kindly sent me the pictures of her polytunnel below. These demonstrate clearly the flexibility of fresh hazel when used in construction.
I have also seen small-bore, plastic drainage pipe and open metal ‘mesh’ used to hold a polytunnel to shape, but definately prefer the hazel as it is not oil derived or using polluting industrial processes to manufacture. Now if only there was a natural alternative to polytunnel lining itself. (OK – glass – but very hard to integrate with natural structures):