The addition of carbon black, PTFE lubricant, mica beads and antimony oxide (particulate fillers in general) to fibrous reinforcements reduced surface roughness. It was also noted that fiber reinforced composites containing particulate fillers yielded lower surface roughness values than the analogous fiber-reinforced composites. A PTFE/silicone-lubricated, glass reinforced polyamide 6/6 composite exhibits a much rougher surface than the analogous composite without the silicone fluid additive. Silicon is possibly causing debonding in glass fiber reinforced composites. The 40% mica/glass fiber reinforced PBT material is much rougher and lower in gloss than the analogous polyamide 6/6 composite possibly due to the improved bonding between mica and a polyamide 6/6. 

Effect of processing variables 
Injection speed, mold temperature and melt temperature all have a significant effect on the roughness and gloss of molded parts.
Fast injection speed always yields a glossier and smoother part, no matter what the other molding parameters were. Filling the cavity as quickly as possible also helps minimize fiber orientation and enhance weld-line integrity. 
A consistent difference in molding was noted between reinforced amorphous and crystalline polymers. For the amorphous materials SAN and PC a high mold temperature is more important in obtaining a good surface finish than a high melt temperature. However, for the crystalline polymers polyamide 6/6 and PBT a high melt temperature is more of a factor in achieving a good surface than mold temperature. This difference between amorphous and crystalline polymers hold true irrespective of parameters were changed. The use of higher melt and mold temperatures in reinforced and filled thermoplastics did not increase cycle times as these materials were stronger and stiffer than their unmodified counterparts, and can, therefore be ejected from the mold at higher temperatures. 
In addition, composites have higher thermal conductivities, which mean that they cool faster than base polymers. A slow injection speed, low mold temperature and low melt temperature are the conditions that will result in the poorest surface texture. 
Designers should recall the following points : 
 • Gloss and surface roughness are related in that a glossier surface is generally smoother and vice versa. 
 • Both gloss and surface roughness are affected by resin type, filler type and loading and molding conditions. 
 • Particulate fillers exhibit lower average roughness than fibrous reinforcements. When they are added to fiber-reinforced composites they reduce roughness. Also, when used to replace a portion of the fibrous filler, particulate fillers reduce roughness at equivalent filler-loading levels. 
 • Silicone fluids act as a debonding agent in glass-fiber-rein forced materials, thereby increasing roughness. 
 • A fast injection speed will always improve gloss and roughness. 
 • Higher mold temperatures are more important for increasing gloss and reducing roughness in reinforced amorphous resins. 
 • Higher melt temperatures are more important for increasing gloss and reducing roughness in reinforced crystalline resins. 
 • For any reinforced composite, the use of fast injection speed in conjunction with high melt and mold temperatures will always give the glossiest and smoothest possible part.