The PX100's are open. Their brother, the PX200's, are closed. The ES7 of course is closed. I have them all, and a Cowon too.
They all sound great, the 200's the worst. (the -II models are supposed to be better)
Anyway you shouldn't wear closed phones nor IEMs under a bike helmet; the only choice is the PX100's .
Comfort, stability, and SQ to spare. Senns gift to the world.
I use ES7 in the gym (where I need a closed phone, and the cups swivel so they pack flat in my gym bag), PX200 on airplanes (again, need closed, but also folding), and PX100 in the hotel room when I travel (SQ is the most important feature, and I want open phones). If I travel in my own car I bring HF-2's for the hotel (cups swivel so they pack flat too) and ES7's (again, swivel flat) if I plan to go to the hotel gym (where again, I need closed).