Magnetic tape   

Audio tape. 

Comes in many widths and formats - from 1/8th” cassette tape to 1” wide 24 tracks.  May also be formated to contain digital information as well.

Magnetic recording tape is made up of several layers:

 
an antistatic backing coating to reduce potentially destructive static buildup during tape transport  a durable acetate, polyester, or polyvinyl chloride (PVC) base 
a layer of magnetic oxide which "remembers" the magnetic fluctuations applied to it by the record head  a smooth top coating to reduce physical wear on record and playback heads 
See also
Drop out 
Print-through 
Saturation