Prefilters are used in filtering maple syrup to create a layered effect. This layering effect ensures the most effective removal of sugarsand/niter from your maple syrup. Prefilters are layed on top of flat filter or inside of cone filters. If you are having problems getting all the particles out of your syrup, you should try using prefilters. Prefilters are available in a variety of sizes and can be cut to accomodate your filtering container or vessel. Prefilters are made of a cellulose polyester blend.