'Synthetic' felt

[2stis]

Wondering if anyone (in the building trade perhaps?) can help me with the name of something and where I might be able to get hold of it please? It is an alternative to roofing felt but looks to be plastic and so last longer. Black on one side and grey on the other, with lots of squares about 1cm wide across it, probably sold in a big roll about 1 metre wide. I know the stuff exists as I have it on one side of the barn roof but the felt on the other side has now perished and I want to replace that to stop the leaks. I have been into a few DIY places like B&Q, Homebase, Wickes, etc. but noone seems to know what I am referring to so if anyone can point me in the direction of a name or trademark for someone that produces it I would appreciate it.

I've got a feeling that once I know the correct name to ask for I may no longer struggle to find it somewhere, but if anyone knows a good place to source it that info would be welcome too! Thanks

[Busa mav]

Look for Tyvek, it is a breathable membrane.

[roofer]

Its called Monatherm made by Monarflex. IKO product. Google and go to roofing underlay section.

[2stis]

Thanks guys. I Googled both of those and now definitely have some good leads to follow up. Cheers