Muslin is a cloth used for numerous things in tech theater. It comes in several widths for all sorts of uses.

Covering Flats.
Covering Platforming.
Covering Trees.
Covering Actors, (costumes.)
Making props.
Curtains.

And much more.

Hint for cutting: Muslin tears in straight lines either across the width, or along the length. Simply make a small cut and then tear the cloth. I tend to make that small cut with my teeth. Just a small tear. Sort of like tearing gaffer's tape.For more info about Muslin, and other theater cloth used in theater, check out the RoseBrand website. RoseBrand is a major supplier of fabrics and painting supplies in New York.

You might want to consider calling RoseBrand and asking about buying damaged goods. They tend to have some damaged muslin almost always and they sell it cheap. I buy damaged goods all the time. The damage? A stain here or there. Since we're always painting our muslin, stains don't matter.

A FAQ from their site: Question: How do I know what weight (wt) muslin to order?

Answer: The three common weights today are light weight, usually used by consumers for a lining fabric or patterning; medium weight muslin, used for hard-covered flats or very small drops; and heavy weight muslin, used for soft-covered flats and larger stops. For drops over 40 feet, we’d recommend using canvas.

Muslin

From Wikipedia, the free encyclopedia.

Muslin is a type of finely-woven cotton fabric, introduced to Europe from the Middle East in the 17th century. It was named for the city where it was first made, Mosul in what is now Iraq.

Muslin is typically a closely woven unbleached or white cloth, produced from corded cotton yarn. "Sheeting" is the name for wide muslin. It is often used to make dresses and curtains. In clothing, muslin breathes well, and is a good choice for hot, dry climates.

The word "muslin" is also used colloquially. In the United Kingdom, many sheer cotton fabrics are called muslin, while in the United States, muslin sometimes refers to a firm cloth for everyday use. In British slang, muslin may refer to women or femininity, while in nautical slang, muslin can refer to a vessel's sails.

Muslin is often times used proficiently in a theatrical setting. It is helpful in masking the background of sets and helping to establish the mood of different scenes. It can be painted to look like countless different settings and if it is treated properly it can become translucent. With the right lighting changes, a backdrop painted on muslin can appear or vanish, allowing a set to be transformed almost instantaneously from one setting to another.

Muslin can also be used as a cheap greenscreen, either precolored or you can paint it with cheap latex paint (diluted with water).