I just got some Aerogel made by NASA. It's the stuff they use to collect space dust
http://stardust.jpl.nasa.gov/tech/aerogel.html and it's pretty close to invisible.
Here's a video I made of it, you may have to open the url directly from media player or divx player cause of the codecs or something.
aerogel.wmv
aerogel.avi (divx)
original file (8.6MB)
Full Size Image
I have more pictures if anyone really wants to see.