How Long Does Black Plastic Sheeting Last?
On the web it is erroneously posted under that question that, "Clear polyethylene sheeting is not recommended for greenhouse use or any other application involving long-term exposure to sunlight. Black sheeting is recommended for applications not exceeding 90 days of sunlight exposure. Special additives are available at request for extended outdoor applications for up to 2 years."
Clear plastic sheeting IS RECOMMENDED for greenhouse use and in some cases has a 10 year UV warranty against UV. See here for the 10 year UV film.
Additionally there are black liners "plastic sheeting" that have a 20 year UV guarantee.