Burns will normally be a result of volatiles in the melt stream not escaping while the mold is filled. When hygroscopic materials are molded with excess moisture content the water will vaporize during plastication and put gas into the melt stream. This gas in the melt stream will normally appear as a splay related defect, but can lead to burning as it tries to travel through the vents in the mold. See Chapter 9 on drying for more information on moisture.