PA66 plastic has a higher melting point in polyamide materials. It is a semi-crystalline-crystalline material. PA66 also maintains strong strength and stiffness at higher temperatures. PA66 plastic remains hygroscopic after molding, the extent of which depends primarily on material composition, wall thickness, and environmental conditions. In product design, the effect of hygroscopicity on geometric stability must be considered. In order to improve the mechanical properties of PA66, various modifiers are often added. Glass is the most common additive, and sometimes synthetic rubber is added to improve impact resistance. PA66 plastic is less viscous and therefore flows well (but not as good as PA6).