The table shows the approximate dielectric constants of a variety of capacitor dielectrics (and a few others).  These are rough averages of numbers from several handbooks and various manufacturer's literature, which sometimes disagree.  Most are for 25C but some are at 20C.
6   Cheap shielded cables are often made with this stuff, but these are only suitable for audio frequencies or low rate data communications.   Quality data cable will generally be made with polyethylene inner insulation to minimize capacitance, or better yet, cellular polyethylene, which is about 50% air. 
Also see:

Dielectric Constants