Hello VitaMan,
You want to use food grade materials. If it is safe for food then it is safe for a product that you grow for consuming like cannabis.
I like to use food grade stainless steel for multiple reasons, it blocks the light, it never gets old and it is safe for your product.
If you are searching for a 1 time cheap fix then I would recommend aluminium foil that you use in the kitchen.
Happy Growing Buddy!