"polyurethane" is the generic term for the bushing material.
"Prothane" is the name of one company that sells bushings and other suspension and chassis products made of polyurethane.
Changing from rubber to polyurethane bushings, stabilizer bar mounts, stab. bar links and other parts can be a double-edged sword.
In the late 1970s, polyurethane suspension bushings were developed for racing applications because "poly" or "urethane" bushings have significantly less compliance than do bushings of rubber. In a racing situation, you don't want the suspension to be compliant.
There are some drawbacks to polyurethane. First, any urethane suspension part will transmit more noise, harshness and vibration (NVH) then the equivalent rubber product. In some cases, the extra NVH is not an issue but, in others, it might be. C3s are already a poor platform isolation-wise. If you're not racing your C3 and you want it to be at least as quiet in side as it was stock, don't use polyurethane suspension parts.
Secondly, the nature of polyurethane is that when it's used in a manner that has it moving against metal parts, such as bushings or stabilizer bar mounts, it squeaks. Yeah, some manufacturers give you this fancy grease to use during the installation but, what they don't tell you is you periodically have to disassemble the suspension and regrease the parts to keep the bushings or stab. bar mounts from squeaking. Some manufacturers of polyurethane bushings and mounts make a graphite-impregnated type of urethane which is somewhat sucessful in addressing the squeak issue. Just the fact that the poly bushing industry developed graphite-impregnating process is proof it knows there's a noise problem with urethane bushings. Generally, I've found graphite-impregnated bushings to be a solution, but only in part. My experience has been that even the graphite/poly bushings will squeak in cold/wet weather.
Some polyurethane bushings makers claim a durability advantage with their products. In theory, the ultimate durability of polyurethane parts may exceed that of rubber pieces and that durability advantage might have some practical applications in some situations--such as the upper control arm bushings on big-block cars but, generally, I feel the life of rubber bushings manufactured from OE or better materials is acceptable on cars that see normal duty cycles and the added durability (and cost) of polyurethane parts might not be of practical value.
IMO, the only times polyurethane bushings ought to be considered is when NVH is not an issue, squeaking is not an issue and the user desires a lower level of compliance in the suspension of a car that is either race-only, a street/track car or a high-performance streeter that gets driven very hard.
If the car is street-driven in a normal manner, on a regular basis by a driver who wants reasonable NVH and no problems with squeaking, OE-type rubber bushings are the best choice.
When considering control arm bushings from which low-compliance along with no squeaking is desired, the Global West "Del-A-Lum" (Delrin plastic/aluminum composite construction) bushing is a better choice than polyurethane pieces. The GW Del-A-Lums are even less compliant than both rubber and urethane parts. In fact, for practical purposes, the compliance of a Del-A-Lum bushing is about the same as a solid metallic bushing or a sperical bearing. Since it is a true suspension "bearing" rather than a bushing and can be lubricated, unless it has failed, a Del-A-Lum will never make any noise. Want more info on Del-A-Lums? See:
http://www.globalwest.net
On my 71 BB Coupe and other cars with modified suspensions, I use some polyurethane in stabilizer bar mounts, stab. bar links, shock absorber mounts, transmission mounts, the front mounts for the C3 rear axle, and the C3 trailing arm bushings. Elsewhere I use the Del-A-Lums in the front control arms and spherical bearings in the C3 rear suspension lateral links (strut rods).
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