Gloss
Gloss is the reflection of light from a surface. The nature and origin of gloss and haze are illustrated in Figure. A high gloss requires a smooth surface. Surface imperfections may be introduced by the processing. Excessive drawing into the strain-hardening region will usually reduce the gloss. Blown film usually has a lower gloss, since crystallisation of the film at the frost-line introduces surface roughness due to the crystals. Rapid crystallization of the film by the use of chilled air impinging on the bubble reduces the size of crystals and improves the gloss. Extrusion cast film passes through chilled rollers after leaving the extruder. The rapid cooling and the polished surface of the rollers provide a high-gloss surface. Extrusion cast films have the higher gloss, but the extrusion blown process produces film at a lower cost. The rheology of the polymer will contribute to the surface of the film. Shark skin is the term applied to a rheological problem in the processing.