Sorry I should have said that the first straps I made were from the nylon tubular webbing purchased at REI. I think around $11 for 30 feet. I purchased that originally because it was easy to drive to REI and pick it up.
I wanted to make some more and I have switched to the polyester webbing mostly becuase I could get 300 foot for $25. I am making a few longer ones for fatter trees. :-) I still have and use my REI Nylon Tubular webbing straps and that is all my sons use. None of us have had any stretch on the Nylon ones used just has huggers not as the main suspension.