Carapils adds body, mouthfeel and improves head retention by adding dextrines, proteins, non-starch polysaccharides, and other body-building compounds into your wort. Carapils is usually used at a level of 5% or less of your total all-grain malt bill. However it can be used at a higher rate in special cases, say if you are making a Session IPA, and are trying to simulate a higher gravity beer. Because of its extremely light color and neutral flavor it won't have much affect on the final color or flavor of your beer. Carapils belongs to a category of malts labeled as Dextrine, sometimes Dextrin, malts. You can steep Carapils in an extract batch but will only get about 20% utilization, or 20% of the goodies of this malt dissolved into your beer.
Briess Carapils Malt