Back in the day, I slept on a sheet of plastic, folded double in lieu of sleeping pad and tent, more or less all year round, mostly on beaches, but just about everywhere else imaginable too.

In about six years if I remember rightly I got through three sheets
Only had one catastrophic fail when I'd laid it down in the dark on a broken bottle. Missed my kneecap by an inth when I knelt on it...

So my longwinded, expert opinion is... two years!