The Green Screen
Green screens are available in all sorts of different sizes and materials. Finding or making the ideal green screen for your application is important so you can get the best results.
The size of your green screen will be dictated by what you are shooting. I have a small screen about five by five feet, which works great for head shots, but is way too small for filming a whole person. If you are looking at shooting a person or another large object in front of the green screen, there is an easy way to determine how big you will need it to be. Set up your scene, or at least a trial run of it. Look through the viewfinder of your camera and see where the edges of the scene are. Your green screen should be larger than the scene itself.
A tightly woven material such as muslin or canvas will serve you best, in terms of being easy to transport and store, but still tight enough to not let light pass through. The downside to fabrics is that they wrinkle and may need ironing to hang flat. Another excellent material is background paper. This comes on a roll and is probably ideal, in terms of being easy to use and not susceptible to creasing in the same way fabrics are. The negative part about paper is that it cannot be cleaned and reused, so it is a consumable product. In addition, if you buy a roll nine feet wide, it can be quite heavy and difficult to transport.
Another option, if you want to create a permanent set-up, is green screen paint. Simply paint a wall the right color and be done with it.