polycro vs heat sheet as ground cloth

How durable do you need? Depends on the ground you cover. I'm often in spruce forest, sharp little needles and no way possible to clear them away. Needed poke-proof, wanted the heat boost. Regular cheap emergency blanket mylar sheets do not stand up to pokes and punctures at all.

Here's one solution from the hardware store: the heat-reflective underlay for floor installations. Your basic mylar sheet, bonded to 1/8" of closed cell foam. Foam side down is very tough, with the bonus of a little added padding under you. Cheap and ultralight. I've now made sitpads from this stuff too.

Another solution: something like the All Weather Emergency Blanket, a true grommeted tarp with a reflective side. You're unlikely to puncture this. Multipurpose advantages as a pitchable tarp and emergency bivvy. Great bit of kit for $15.

Polycryo is more durable for it's weight. You can find them for less than $5 at many hardware stores in the US sold as storm window kits.

The light weight and invisibility can be annoying to work with in windy situations though.

Tyvek is even more durable and easier to work with, but weighs significantly more.

Polycryo is definitely more durable for a groundcloth.