Do you want plastic sheet, rather than weed suppressing fabric?
Plastic is solid, water and air can't get through, weeds can't get out!
Weed suppressing fabric is a mesh, water and air can get through, MOST weeds can't get out.
Plastic might be used for clearing a plot initially (e.g. instead of weed killer), but I think weed suppressing fabric is preferred for pretty much anything after that.
Sorry, don't know the "grams-per-square-metre" that gives you something that keep the light out, weeds down, and you can, for example, walk on without puncturing.