This stuff is a must have, it's used extensively in the TV and Film industry and it's got numerous uses for light manipulation, flags, gobos, snoots. It's basically a stiff tinfoil with black paint covering both sides, comes in a couple of widths 1 ft or 2 ft and 25 or 50 Metre lengths, either from Lee Filters or Rosco. Whatever you do, don't use it to cover the Sunday roast, the paint will probably kill you. It's really useful stuff, instead of using a snoot that just give you a round aperture the foil can be moulded into any aperture shape you want, within reason. A quick snip with a good pair scissors and you can create godos, hang a sheet of it from a stand and you've got yourself a light weight flag, it's just a great shadow FX product. I've always got some with me, whether I'm in the studio or on location, it's one of those essentials like gaffer tape or blue-tac, it's always in my accessory kit.