180 days.
It also depends on the environment it is stored. Some materials can become brittle or decay is certain conditions and also some can crease in place and not be as flexible.
Sun, temprature fluctuations, debris like sand and dust....
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2520105-2D.pdf&ved=2ahUKEwiRj8muoI7vAhVdyDgGHeAlChIQFjABegQIAhAG&usg=AOvVaw0CdovsNL9l20Ccrs8QBOfi
AC 105-2D.pdf