Batting is rated by what is called loft. The higher the loft the fluffier the look on the finished quilt. Cotton batting behaves differently than ployester batting. Some battings shouldn't be used for baby quilts, because of the way they react in flammable conditions. ( This is usually listed on the batting parceling) A good way to "see" how batting differs is to check the different batt styles at your quilt shop and feel them. It will give you an indication of the texture that will be a part of your quilt when finished. one layer is usually enough unless you are specifically trying to achieve a design look..ie Trapunto, or stuffed, or extra padding. All of these styles are able to be found in books or even taught at your local quilt shop. For more info you could check out this site : http://www.stearnstextiles.com/[b]. Hope this is helpful. :-)