Do third party replacement tips fit on the apple in ear headphones? I prefer foam tips as they block out much more sound, but I'm not sure if Apple use the standard fitting for headphone tips!?!?!?!

I beg to differ :- http://store.apple.com/uk/product/ME186ZM/A/apple-in-ear-headphones-with-remote- and-mic?fnode=49

Agreed. Now, does anyone know the answer to the original question?

Ideally I'd like to use Comply tips. Will they fit?

Answer found. Please find below an amazon review explicitly mentioning adding third party foam tips. Sounds like they fit and work like a dream:

"As a audio engineer, I own about a dozen different sets of earphones and in-ear 'phones. My favorite, by far, are my sure SE530s. I have some Sennheiser cx400s which are good workhorses, but lack the finesse, clarity and stunning accuracy of the Shures. For convenience, I bought the Apple's, as I wanted something I could use with the phone for calls.

I found the sound to be quite clear and beautifully clean, but like many, no matter how I tried, the stock Apple tips never made a good seal. The seal is absolutely essential to getting bass out of a balanced armature design. For you non-engineers, just trust me that if you don't have a proper seal, you will have no bass.

In my case, I think the trouble had to do with the largest size being a tiny bit too small, and the silicon being too rigid, yet slick, so they left small airgaps and were easy to remove. I tried using some foam tips from a third party, but their large was more of a medium, and never came close to a snug fit.

As an experiment, I dug around in my ear-tips from my Shure's and tried their rubber tips which are about the same size as Apple's large tips, but made of a more pliant and slightly sticky rubber.

OMG, what a transformation. Suddenly the sound blossomed, the bass became rich and well balanced, and the "top-heavy" sound was totally mellowed into a rich, well balanced and incredibly detailed presentation.

Make no mistake, these are the best 'phones under $200 I have ever heard. The bass is deep and warm, very detailed, and totally lacking fuzz or buzz that I can hear in the Sennheiser set. Look at getting tips from a better headphone. The trick is it has to have a soft rubber base that can expand over Apple's slightly larger stub. Some tips, like the Shure foam tips, have a rigid plastic sleave in the tip to keep it's position correct, and these won't expand over the larger Apple posts."