An example would be caprolactam in nylon. Sometimes this unreacted caprolactam will result in a white buildup on the mold and/or part surface. This buildup in vents will lead to burning of the part, and the white buildup on the part will be a visual defect. Due to a wide range of moisture content in nylon and its low viscosity it can be challenging to provide adequate venting to allow all volatiles to escape while the mold is filling.