full link: http://www.youtube.com/watch?v=HoCAxS4vqwQ
From the above video's caption:
There is also now a metal that is even lighter than aerogels:This is the lighter than air solid developed in the 1980s, based on agar, a derivative of seaweed.
During manufacture, the internal foam space can be filled with a variety of gasses, including helium or hydrogen and the material is then shrink wrapped to prevent leakage.
http://news.yahoo.com/worlds-lightest-s ... 09070.html
NASA is very involved in aeorgel technology:
http://www.nasa.gov/topics/technology/f ... ogels.html
It looks possible to me that some of the solid objects we see floating in the ISS videos could be made of these substances. The floating effect might also be enhanced by mixing in a heavy gas with the air that the ass-tro-nots are located in. This technology, plus CGI, video compositing and "wire work," might comprise the range of weightless effects that we're seeing in these videos.