Greenhouse Shading - What do you use?

[Creemteez]

Being a dreadful old skinflint, I use the blue recycling bags that were provided by the council till they replaced them with mini dumpy-bags. Split down the length and opened up they are just the right size to cover the roof glazing taped into place with a bit of polytunnel repair tape. I tried the red ones but the sunlight bleaches them.