Home Depot in Canada doesn't carry the right type of poly commonly used in green house glazing. They sell polyethylene sheets used as moisture barriers. They do have a thicker one (I think it's 6 mils) which I use for my unheated greenhouse. It's not UV proof, and I replace it once every 3 years. Ideally I should be using 150 microns, UV inhibited sheets, but they cost more.