N.O.S. Rubber vs. EPDM

The one thing that would make your 1962 project car complete is a set of N.O.S (New Old Stock) window rubber from the early '60s. You've been scrounging the swap meets for months until you finally found some still in its original box. After you pay too much for it (after all, it is N.O.S., right?) you install the stuff and think your car is pristine. But wait, after about a year, your expensive N.O.S rubber is cracking and starting to curl. What gives? It's N.O.S., right, and N.O.S. is the best, right? Not exactly.

First of all, back in 1962 when your car was made, rubber technology was nowhere near what it is today. What you wrapped around your windows was a direct derivative of a rubber tree that stood in an equatorial jungle, extruded (squeezed through a mold) and glued together at the ends. Just like a 30- or 40-year-old tire, original rubber will crack with age. And who in their right mind would run a 40-year-old tire on their car?

Available now is a much better rubber than N.O.S. window rubber, and it's called EPDM. EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber--a highly flexible stable material--a terpolymer of ethylene and propylene. It has a saturated polymer chemical "backbone," which gives it excellent resistance to ozone and many other advanced chemicals found in today's environment. EPDM's balance of physical properties and chemical resistance makes it ideal for a wide variety of rubber applications, especially window seals. Other characteristics of EPDM rubber include excellent color stability, heat resistance and dielectric qualities. As well, it offers many of the advantages of rubber at a lower cost. EPDM rubber is slightly lower than both natural rubber and polyisoprene in resilience and tensile. However, it is not recommended for applications involving petroleum derivatives such as mineral oils, solvents and aromatic hydrocarbons. But, for window rubber, nothing beats it.

Be forewarned, however, that not all EPDM is created equal. It's like a rubber alloy, and it can be mixed in many different forms. As a general rule, the clearer the base mix is, the better the EPDM quality will be. Some will be less ozone and smog resistant than others, depending on the mixture used when making it.

As in most everything, you usually get what you pay for. Ask your supplier what kind of ozone and smog and acid rain resistance their rubber has. While no one wants to give out their "special" EPDM formula, all of it will most likely be better than the original, window rubber.