The picture is of Laen, sporting a 33 gallon sized Hefty cinch garbage sack weighing 1.6 ounces.
I often wear mine even if I’m wearing rain pants, because it has been my experience that all rain pants eventually leak but a trash bag is dependable.
Some people make or buy a rain skirt out of sil-nylon. They are more expensive, less water proof, and heavier.
I’m thinking of improving my garbage bag skirt with a better cinch cord. I’m also thinking of trying out the 39 gallon size for a longer skirt.