Muslin comes in many widths and weights, and is available in NFR, FR, and IFR versions. Heavy-weight cotton muslin is primarily used for drops and cycs. Drops can be made from either Fire Resistant (FR) or Non-Fire Resistant (NFR) fabric. NFR fabric is useful because there are no FR salts to interfere with the paint binders. However, the drop must be coated with a flame retardant chemical after painting, or a flame retardant chemical such as Rosco’s P50 must be mixed into the paint, to make it NFPA compliant before use. FR and NFR muslins are identical except the FR version is pretreated to meet NFPA standards.