Now that's a different one. looks almost like a softback.
With a new to me carpet backing, I always used to test it out by setting my seaming iron on 3.5 or maybe a little higher, then once fully heated, I'd set the iron directly on the backing for maybe 5 seconds or so. Some backings could handle it and some would shrink, distort or melt almost instantly.
I'd at least have a starting point knowing it's sensitivity.
I'm thinking a low temp urethane tape for that one .