Down alternative comforters are usually made with a synthetic filling, such as MicroMax or PrimaLoft, although lambswool filled comforters are available. For those who have severe Allergies but would like the feel of down, a hypoallergenic down (brandname HypoDown) is also available. Every company is going to make it a little different. Synthetic fibers, wool, and silk are common. Anything with real down, even if it says allergy-free, is not going to work everyone.