I travel a lot. The hours spent droning through the sky can be made more tolerable with an MP3 player and a set of noise-cancelling headphones. Reducing the sound of the airflow and engines is a great relief.
For a year or two, I used a pair of folding Sony MDR-NC5 Noise Canceling Headphones, the ear foam covers self-destructed. I replaced them with old washcloth material and was happy, but the DW thought it looked bad. I switched to a new set of Sony MDR-NC6 Noise Canceling Headphones. These worked equally well, although they did not fold as small as the MDR-NC5 headphones.
Over four years of use, the MDR-NC6 headphones started cutting out and making popping noises. This was not surprising considering the beating they took on travel in my backpack. It looked like I needed another new set.
The older MDR-NC5 headphones were still on the shelf with the hated washcloth covers. A quick search online showed a vibrant business in selling replacement ear foams, often at exorbitant prices. Nowhere did I see ear foam covers made for the oblong MDR-NC5. I then realized that foam is stretchable and that the shape should not matter. After another search and some consideration, I purchased 2-5/16" foam pad ear covers that were able to stretch over the MDR-NC5's strange shape. Problem solved for less than $5.