Synthetic yarns generally tend to melt though some synthetics are inherently flame-retardant. The estate's largest unit is Indo Rama Synthetics, which manufactures synthetic polyester yarn. Its fibers are very resilient compared to both other synthetics and natural fibers. There are many concerns about the life cycle of synthetics, which come primarily from petrochemicals. Roofs coverings include asphalt and synthetics. Many synthetics are also UV inert. It is more hydrophilic than most other synthetics, allowing it to wick away perspiration. PLA is more resistant to ultraviolet light than most other synthetics. Velodrome tracks can be surfaced with different materials, including timber, synthetics and concrete. Common media materials include&colon; sand, granite chips, slag, steel, ceramics, and synthetics. PAO oils (group 4 synthetics). Nootropics can be further classified into two categories&colon; synthetics nootropics and natural nootropics. Guano was considered a good organic fertilizer, prior to the use of modern synthetics. Foster roofed the main railway station with translucent Teflon-coated synthetics. Each of these companies patents several processes for the production of aromatic synthetics annually.