Sensaphonics seal test:
Also it's not the earphone that blocks out noise (unless it's open ported like the JVC FX500 / FX700 = detrimental to isolation but increases bass reproduction), it's the eartips. e.g. Shure Olives, Monster SuperTips [ovepriced to the max if you don't buy an Monster IEM and want to buy them separately), Etymotic tips, foam eartips, Comply eartips are all known to be great for isolation. Experiment with all the bundled tips that your super.fi 3 includes and use the ones that fit your ears the best. your ears via heat will mold around them.
Actually the earphone itself can play a role. The material choice can possibly transmit sound. Also the design of the housing can come into play as well. The MC5 for example is slightly better at isolation than the ER4 IMO because the larger housing plugs the whole canal entrance whereas the ER4 allows space around the housing.