Mylar is a paper that is coated with or made from a polyester film BoPET (Biaxially-oriented polyethylene terephthalate). Mylar isn’t the polyester film itself but the brand of BoPET manufactured in the United Sates and UK. Mylar can be stretched for a long period of time without breaking. Its reflective nature makes it a great tool for decorative projects as well as many other practical uses from bags of chips to gift wrapping.
One of them is often used by Directors on set who need "dancing lights". They can achieve the trick on the cheap.
Take a large sheet of Mylar paper found in stationary stores, attach it on a bar/ stick so it is suspended and free to move.
Cut strips of similar sizes from top to bottom. The nature of Mylar will curl those strips and become rounded.
Use a small fan on one side to make the strips dance while using a projector on the other side, beaming its light to the dancing strips. The reflection of the light on the strips will give a moving effect that can be used on a wall or objects/people moving or not.
The imagination is limitless on how to use this inexpensive technique.