Oh man was I wrong -> ripped from
csp.com
CAT5:
Ratified standard for unshielded twisted pair. Handles voice or data at 100MHz over 22 or 24 AWG wire. Used for high-speed twisted-pair networks such as 100 base-TX, fast ethernet.
CAT5e:
More stringent specifications than CAT5. CAT5e has a higher rating, 350Mhz vs 100Mhz for CAT 5...it also provides better performance. Cable manufacturers have improved the cabling, connectors and patch cords of regular CAT5 to provide an improved attentuation-to-crosstalk ratio (ACR), and to meet or exceed all the parameters of the CAT5e standards approved by the Electronic Industries Association/Telecommunications Industry Association (EIA/Telecommunications Industry Association) and the Institute of Electrical and Electronics Engineers (IEEE)
OK - the thing that I was talking about is plenum - it's just the coating around the twisted pairs - it doesn't do anything with metal -> it does protect from heat sources though and it costs triple the price of regular cat5e cable.
sorry for the confusion!