usually they are made of cotton, but it can vary between other light materials that are able to soak up liquids.
It is a type of fiber, sheeps hair that is spun into threads or yarns and then used to make a fabric.
The fabric you are asking about is called knit or fleece. Fleece is the original type of fabric used for hooded sweaters, using real lambs wool, but it now simply a name of a fabric used in the garment.
Stockinet
Fabric panels can be used for a multitude of things. One of the best uses for fabric panels is to make quilts. Fabric panels can also be used to make creative gifts.
Denim is the fabric most used to make a pair of jeans.
DuPont's Nomex is called an aromatic nylon.
Boski is a type of fabric that is commonly used in South Asia, particularly in Pakistan. It is a fine, lightweight fabric made from a blend of silk and cotton or synthetic fibers. Boski fabric is often used to make traditional clothing such as shalwar kameez and kurta pajamas.
Linen is a type of fabric that is woven from fibers of the flax plant, and is used to make modern garments in textile imdustries.
The fabric used to make flamenco dresses is silk and polyester
Bosky fabric is the term used to describe Chinese silk. This type of fabric is typically used for suits and other fine garments.
Horse fabric is used to make items such as brushes for painting, upholstery and strings musical instruments. It is usually referred to as horsehair fabric.
Lizibizi is a brocade fabric that was used in the Renaissance era. The fabric was often used to make shirts, pants, and linens.