From the Internet:
"There are four main varieties of muslin available in the market.
Gauze: This type of muslin is ultra-lightweight. It’s the finest and thinnest fabric so far. We used this muslin for clothes, filters in the kitchen, and dressing pads for wounds.
Mull: It’s a lightweight and plain muslin. This muslin is made of a fusion of cotton & silk. It’s heavier than gauze in weight. Furthermore, it has uses in dress underlings—a layer of fabric underneath your main fabric and pattern testing for garments.
Swiss Muslin: It has raised patterns and dots on the fabric. This muslin is perfect for usage as warmer clothes.
Sheeting: This is the thickest and coarsest type of muslin available so far in the market. It’s often used for furniture upholstery, home wares, hardware, and backdrop."