I was always loosing the rubber earpieces from my Sonys, so I found some reaplacements, which actually work better (to my ear)
Step 1: Buy Earplugs
I found these ear plugs at a local camping/outdoors store. They're designed to reduce outside noise by using a removable plug to antentunate either high frequencies (in-flight noise) or low frequencies (snoring)
I use them for work because I sometimes spend periods in a loudly air conditioned server room.
The plugs are made by a company called "Design GO" and cost 6UKP
Step 2: Cut the Stalks
After removing the little plugs (yellow in this photo - they're the LF plugs) from the earphones, you're left with a rubbery bit of silicone.
You'll have to cut a little of the stalk (ie - the tube of rubber the plugs go into from the back. Otherwise, it's too floppy to get inside your ear properly.
Step 3: Attach to Earphones
The Sonys are quite a bit bigger than the hole in the plugs, fortunately, the rubber stretches well, and if anything it helps keep the plug and earphone together.
Fold the flanges of the plug back, and work the rubber over the little pole that contains the speaker. It's easier if you get one side on, and then pivot the thing over.
Once the rubber is totally over the plug, work it back as far as you can, and that's it!
Step 4: Job Done!
I found the bass was much better, and the sound isolation was pretty much 100% (which isn't a surprise as this is what these plugs are designed to do)
One word of warning, while using these headphones, you won't be able to hear things around you. Pay more attention to traffic while walking, and for bob's sake, don't wear them while cycling!
This is my first instructable, hope you liked it!