This is a very clean, light-colored rubber. To prevent enzyme darkening of the rubber, 0.05% of sodium metabisulfate is added at the latex stage. SMR L’s primary use is in colored compounds, especially light or bright colors. The clean, consistent rubber allows less colorant to be used as well as improving the batch-to-batch uniformity of the color (this week’s color will match one made 6 months from now. Non-color-specified rubber does not lend itself to this consistency). The low dirt, etc. also results in high quality physical properties as well. For strictly physical properties, most compounders might choose the slightly less expensive SMR 5 which is clean but not as good a color. However, it doesn’t make sense to carry two forms of the same product if SMR L will cover all requirements As most compounders know, use of a precrosslinked rubber, whether synthetic or natural, offers a variety of processing advantages. Precrosslinked natural rubber improves processing without impairing the finished physical or functional properties. In fact, blends with SBR will have improved physicals as is typical with NR addition to SBR while providing the smoother processing. The table below shows varying levels of PA-80 mixed with SMR L. Physical properties are consistent throughout. At 40 phr of PA-80, the extruder die swell has been reduced by 67%.