Slippery tree straps--what's the solution?

[Pipsissewa]

I bought a new set of tree straps recently and they are obviously thicker, more densely woven and stronger than my mule tape straps and my Hammock Bliss straps. The nature of the webbing is exactly like a seat belt out of a car--sort of silky and slippery. The thing is this: they won't hold tight. I cinch them around the tree trunk, they fall loose. I make a marlin spike hitch around my toggle, the toggles slips right out...Super annoying! Only the tension of the hammock completely set up keeps things from sliding.

Is there some sort of sticky treatment I can apply to fix this? Like tar or wax or something like that? Or should I just accept the way they are, in which case, I'll probably go back to some other straps because I can't stand this!

Thanks in advance for your help!