LISA M started off this discussion years ago.
Wormy the editor has updated it:
Question: Do we need a projection screen?
Answer: Probably not.
Projection screens were all the rage for many decades when film projectors ruled Sunday School. They were necessary, in part, because of lack of wall space, and the low light of projectors. The reflective coating of the screens helped the image look better.
Today, we use LCD projectors which do not need a special screen, and in fact, don't look right on old movie screens. instead, you just need a RELATIVELY FLAT WALL.
The wall can be either white, off-white, or sand. Colored paint will make some of your projected colors look sick.
Sheets are a good temporary fix, but get saggy.
In some situations, you can buy a LARGE VINYL PULL DOWN BLIND at the home improvement store and use that as your projection screen. Mount it to brackets and up she goes when not in use!