Well, actually it's more like the equivalent of eight large plastic bags.
The basic technique is to fuse thin plastic together using an iron and some baking paper to stop it sticking. This creates a strong tarpaulin-like material which can be sewn together.
The technique itself is well documented elsewhere (such as here by DIY genius Bre Pettis). I wouldn't recommend it as a great way to make clothes - unless you like wearing scratchy, stiff garments. However, if (like me) you have a friend who needs a costume for a recycled fashion show, then go crazy.
There's definitely some things to bear in mind though.
- The plastic shrinks as you heat it - you'll need to start with much much larger pieces than you think. Also, fuse all your plastic together before you cut out your pattern pieces otherwise you'll end up with mismatched shapes.
- The shrinkage issue also means it's tricky to iron after construction. You can do small repairs but be careful. Keep the iron on low and moving at all times.
- The plastic has absolutely no give whatsoever so think carefully how to get in and out of your garment. I had to use a side zipper and fasteners on the shoulders to get the fitted look.
Lastly, you might want to think about using your least favourite iron and ironing board. Baking paper is slippery stuff.