Fuel resistance of foams & sponge rubber-an explanation

In regards to unleaded 90 octane petrol or road rated diesel it is true  little or no degradation will occur if you were to splash fuel onto the PE, EVA, neoprene or EPDM & then wash it off within an hour. Some surface cracking however might occur if it was not washed off in a reasonable time.

The correct definition of calling a foam or sponge “fuel resistant” however is defined by the SAE (society of automotive engineers ) & they have a standard test (SAE J18 ) which measures the degree of “swell" in sponge rubber (Neoprene & EPDM) or foam plastics (EVA & PE), when they are exposed to fuels. This “swell” is indicative to the degree of stress cracking that will occur to a product over time. Stress cracking is the process of degradation or in simplistic  terms, product failure.

Neoprene rubber swells less than 150 % when tested to SAE J18 where as  EVA & PE foam will swell to 896% therefore EVA & PE has nominally 6 times the likelihood of failing - But the effect is exponential so in fact it is more like 20 times and if you add heat to the equation & it is even worse.

To claim, as some do, that EVA or PE foam is fuel resistant is therefore very dangerous & exposes you to incorrect material selection & subsequent application failure. If fuel exposure is likely, choose neoprene sponge rubber.