Thanks Leclused - but I live in the Yorkshire Dales; we don't have thrift stores selling wetsuits! They would almost certainly be double lined anyway but I need single lined to make a neckseal.
Thanks Ian P - but ?20 delivery charge seems a but steep for just a bit of neoprene. I'd really prefer 4 mm as well, for home build.
Thanks Benfool - but I specifically want the neoprene rather than a ready made up seal (as I find commercially available ones don't fit that well, unless you actually go and explain requirements in person).
Anyone got any other ideas?