I don't know about the thread. I do know that my X5 cover went through summer and winter outdoors for three years with no visible sign of deterioration. A quick call or email to them will give you an answer I'm sure.
"For every complex problem there is an answer that is clear, simple, and wrong." (Henry Louis Mencken)
2005 X2, Viper Red, MCX, Acme 1285, PPass
(previous) 2001 X5, 1991 TriStar 190