Plastics used in molding toroid mounts and headers come in two broad categories, thermoset and thermoplastic. Thermoset plastics include epoxies, phenolics and Diallyl Phthalate (DAP) which are known for their environmental stability and ability to tolerate over 750° F without melting. Thermoplastics include nylon, polypropylene, polycarbonate, polyester (Valox, Rynite), LCP (Vectra) and PPS (Ryton) which will begin to melt if they experience temperatures much above 500° F for an extended period. The chemistry that gives thermoplastics a lower melting point also make it less expensive to mold, giving it a cost advantage over thermoset plastics.
Thermoplastics are widely used in applications that do not experience temperatures above 500° F, except for a few seconds during the winding lead to terminal and component to PCB soldering process. Thermoset plastics on the other hand, are popular in magnetic applications when it is used in conjunction with self stripping magnetic wire. The un-stripped and un-tinned magnetic wire is wrapped around a terminal molded into a thermoset header or toroid mount and then dipped into a 750° F solder pot. The high temperature solder will burn off the wire’s insulation, tin the wire and solder it to the terminal in a cost effective way, without melting the mount.
There are trade offs between the two plastic types that must be considered. The mount will be less expensive if molded from thermoplastic but will require pre-tinning the winding leads and careful heat management while soldering the leads to the mount and soldering the mount to the circuit board. The thermoset mount will be more expensive, but with self stripping magnetic wire, several terminations can be soldered at once and the wire will not need to be stripped or pre-tinned, possibly making the overall cost of producing the component lower.