Splay is a term used in the manufacture of injection molded plastics to refer to off-colored streaking that occurs when moisture is caught in the material feed, or if the material degrades during processing. That degradation creates a gas, which is the cause of splay. If cold material impacts the surface from filling at speed, jetting may appear, which looks very similar to splay.
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Splay (plastics) Wikipedia(Text) CC BY-SA