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Polypropylene, more commonly called "poly" or "polypro," has a wide range of chemical compatibility (resistance). It can handle many phosphoric acids, up to 40%, aggressive ag chemicals, soaps, waxes, and much more. This expansive chemical coverage is why polypropylene is so widespread.
Products that should be avoided when using polypropylene include Nitric Acid, Bleach, and Chlorine. In addition, Creosote should be avoided due to the relatively low-temperature range of polypropylene. Oil based products such as hydraulic oil, kerosene, and diesel fuel are not recommended for polypropylene either. While most of these products can be transferred through polypropylene, over time the solution would erode the fittings and render the plumbing system useless.
Polypropylene fittings are extremely diverse and can be used in a wide variety of applications. Most poly fittings are low pressure, meaning they have a working pressure of 150 PSI or lower. These fittings are injection molded using a die-cast to form the various sizes and shapes required. This plastic can be dyed virtually any color. Polypropylene is the second most produced plastic, only trailing polyethylene. Polyethylene is fairly similar to polypropylene; the most notable differences are different chemical compatibilities and temperature ranges.