Ground Cloth or Pad?

Polycro, from GossamerGear is tough and lighter than a pad.

You can also buy the window film from Ace Hardware, WallyWorld, etc and cut to size.

Thats what I was refering to with the 1/8" foam. Is there anywhere to buy those full length? The question still remains: wich is more effective, the foam or the groundcloth.

groundcloth

More effective for what? If simply keeping out water, polycro (window film) would be better and lighter and cheaper (on sale @ Walmart now). However, if you have an inflatable pad, you may prefer the CCF under it as added protection for your PCT hike. It will also add a bit of insulation.

A groundcloth is really more for keeping your bag and bivy (or tent floor) clean and dry. A polycro or tyvek sheet will not provide any insulation.

A sleeping pad is for insulation and comfort. A thin polyethylene pad (like a Thinlight from Gossamer Gear) is mostly for insulation, not much for comfort. Thicker foam pads (like a Ridgerest) or inflatables (like a NeoAir) provide both insulation and comfort.

Most people seem to take both as they really do different things. For the PCT, I think I'd take a polycro groundsheet and a foam pad like a 3/4 length Ridgerest or ZRest.

I use a 1/8" foam pad as my snow camping groundsheet. It adds a little warmth at very little added weight (like 1 oz more than a polycro for 30×74). But for summer use, every sharpish object ( pine needle, pine cone, etc.) sticks to it so it's kind of a hassle unless you are always on sand or smooth rock slabs.