A good lightweight comforter should be made of high quality materials that are designed to keep you warm without being too heavy or bulky. The fill material and the type of fabric used for the shell are important factors to consider when choosing a lightweight comforter. Down and down alternative fills are popular choices because they offer a good balance of warmth and weight. Microfiber and cotton fabrics are also popular choices for the shell of a lightweight comforter because they breathe well and provide a soft, comfortable surface to sleep on.