Any given screw geometry is not going to be the correct geometry for every material. For materials that are shear sensitive high compression ratios may lead to degraded material The screw L/D can impact material degradation and lead to brown streaking. L/D refers to the screw flighted length over the diameter of the screw. Larger L/D ratios can provide more gradual application of shear to the plastic. Although a larger L/D (greater than 20 : 1) provides a more gradual introduction of shear it can also lead to longer residence time that could cause brown streaking.