I have had some success with Tyvek tape, which is a bit on the expensive side. Polycryo as is called here, is a mix between polyethelyene and polypropylene (olefin).
These two plastics share certain similarities, both are very slippery, chemically stable, and very hydrophobic. It's hard to bond anything with them, except for a rare couple of ways.
Since Tyvek tape was designed specifically for Tyvek which is made out of polyethylene (the high density kind), and since i've used Tyvek tape with good success on Dri Ducks and Frogg Togs material, i figured it would work decently with cross linked poly olefin material, and it seems to work well. I did not do tests like some others here did though.
I had made a tarp out of a sheet of "polycryo" with a polyethylene reflective heat sheet bonded to same.
It's a decent tarp, but since i do most of my backpacking during late fall, winter, early spring when it's colder (like the cold, not so much the heat), i have since realized that a more wind resistant shelter is for me, so i went with a used cuben solomid i got from here. I'm giving it to a friend for their bugout bag.
I've had ideas of reinforcing polycryo with one of the super light woven nylons (which have much higher tensile strength) and creating a more true two walled shelter material, but since i have a good shelter now the motivation to spend money on an experiment i'll likely not use isn't really there. But the idea is to over lap say Titanium Goat's Nobul fabric with polycryo, roll/fold over the edges a few times, and sew that with a semi long stitch. Obviously the polycryo would face outwards for water protection and the nylon would go inside. The edges (which would be exposed nylon) could be sprayed with silicone so they don't absorb as much moisture.
While this could be both a bit lighter and more condensation free than silnylon, it will be a bit more expensive and definitely less durable than cheaper silnylon.
So, not too sure it's worth it, unless you want a little extra warmth or no misting and less condensation. Part of me is tempted to try it anyways, just to see how well it works or doesn't.