These plastic vials and inserts are made with “ultra-virgin” polypropylene and are specifically suited for LC-MS. What this means is that the material is made of a proprietary polymer which is free of extractables that could cause baseline noise in LC-MS analyses. The plastic is not recycled and is not re-processed. Many other manufacturers use mold release agents, clarifiers or antioxidants to the formulation which allows for rapid removal of the vial from the mold during production. The drawback is that these agents can present issues as impurities in the finished product; see related article below.
Hence, “ultra-virgin” polypropylene do not use these agents and are therefore made to a higher standard of quality.