WOW! Got a pair of Cambridge Audio A-100s as a gift. The silicone tips they came with were extraordinarily thin, so they didn't seal well (at least in my ear canals). Both the ANC and audio performance were so unfortunate, that I was strongly considering returning them. Then I ordered and received you ear tips (which I've been a satisfied user of since my days with Audeo and Westone wired phones). WHAT A DIFFERENCE!! They sealed to my ear canals right away. The audio difference was astonishing! Music which I listen to regularly suddenly produced goosebumps again. And the ANC now worked flawlessly, sealing out extraneous noise, even TV sound where the TV was in the same room I was listening to music in.
And, in case you were wondering, they fit perfectly in the case and do not interfere with charging of the earbuds.
In my opinion, these are an absolutely mandatory accessory for the Cambridge Audio A-100s.