<a href="https://en.wikipedia.org/wiki/Aerogel" class="extiw" title="en:Aerogel">Aerogel</a>: Though with a ghostly appearance like an hologram, aerogel is very solid. It feels like hard styrofoam to the touch.
Courtesy NASA/JPL-Caltech
between 1994 and 1999 <div style="display: none;">date QS:P,+1994-00-00T00:00:00Z/8,P1319,+1994-00-00T00:00:00Z/9,P1326,+1999-00-00T00:00:00Z/9</div>
<a rel="nofollow" class="external text" href="http://stardust.jpl.nasa.gov/photo/aerogel.html">NASA Stardust Website</a>