Hey Darwin, Those look pretty cool!
I had a pair of earbud speakers from Radio Shack which worked on a similar principle of the expanding foam design. I used them with my MP3 while snowmobiling. It attenuated the outside noise marvelously, but was hard to assemble and get comfortable with.
Of course, when one is sledding you have a helmet and a liner to deal with and occasionally people want to talk with you and it is hard to communicate, so I would only rig up like this when riding alone and for long distances.
In the plane, would/are you inclined to use them even for the short hops? Are they easy to get comfortable in? For a short hop, are you likely to just grab a headset and go?

CJ