EPDM has these advantages over NBR:
- Better aging resistance
- Better ozone resistance
- Better temperature resistance
- Better chemical resistance
Now that looks great on paper until you dig into the numbers of both chemical compositions and their use cases.
Better aging resistance: According to DIN 9088, which stipulates the storage life of rubber products, NBR is a class 2 product, while EPDM is a class 3 product. EPDM has a shelf life of 10 years, while NBR has a shelf life between 10 and 6 years, depending on the item (hoses are generally allowed shorter time frames for example). Is that really a concern for us in the SCUBA industry as end users? I don't think it is.
Better ozone resistance: This falls into the same aging category for me, as ozone will attack a material over time. EPDM is clearly better at withstanding O
3 and thus lives longer. However, we probably rebuild our regulator long before that becomes an issue. So is that something we should concern ourselves with? I don't think it matters.
Better temperature resistance: EPDM is usable in the region between -50°C and 150°C, while NBR is usable somewhere in the region between -30°C and 140°C. Yes, EPDM is better than NBR, but does that matter to us when the temperature range is already sufficient? Furthermore, EPDM burns much hotter than NBR, making it a worse choice for oxygen service. EPDM is
NOT suitable for oxygen service, just because it can withstand slightly higher temperatures, just like NBR isn't. FKM is the only viable option.
Better chemical resistance: It depends on how one defines chemical resistance I guess. While EPDM has a much broader range it can work in, it isn't better in all situations. It mostly excels in acidic environments when compared to NBR. But NBR has superior fuel resistance for example. But again, does that matter to us in the SCUBA industry, where we only work with nitrogen, oxygen and helium? Neither material is suitable for oxygen service anyway.
And here comes the final straw, while I think the EPDM "hype" is misplaced in the SCUBA industry. In terms of mechanical resistances, the materials are nearly identical. Their abrasion resistance, compression set and other mechanical properties are virtually all the same. Some sources will place EPDM ahead of NBR, while others place NBR ahead of EPDM in terms of mechanical resistances. From my own personal experience, I find it hard to tell a difference at all with regards to mechanical properties.
Now all that written for what I believe should be a simple conclusion: NBR is just fine for this. EPDM is not inherently superior to NBR in the SCUBA industry. It has its place in certain circumstances and manufacturers historically jumped onto that "hype" wagon a long time ago. The reasoning back then was superior oxygen compatibility, which turned out to be false. Most if not all have slowly backed off from it and use EPDM in places where it makes sense, not placing it everywhere.
