Of the nonwoven polypropylene I had on hand, I found it was best use 3 to 4 layers of the car cover which is around 100 GSM per layer and then one layer of a surgical gown which is about 50 GSM.
As a loose guide based on my research car covers are about a 100 to 150 gsm. Shopping bags are 80 to 100 gsm. Disposable painting overalls and surgical gowns are a bit lighter and about 30 to 50 gsm.