Do you mean storage tanks like these?
http://www.pneuaire.com/reca44cuin.html
These are a great way to cut down on weight! we took off around 5 lbs from our robot this year from switching to these. R3P0 from 1504 put the specs as far as he could remember on here
weight .50 compared to .88 ( roughly from memory)
cu in 44 compared to 16