What material to use to surround hard drives?

[taisingera]

I took out the hard drive cage from a Antec SLK3700 and would like to put some SATA drives in it to use as external storage (BTW, dumped the case). Should I leave the drives bare or what can I surround the cage with to protect the drives? I plan on mounting a 120 mm fan on front to keep the drives cool.