BASF, the big German chemical company, defines plasticizers thus:

"Plasticizers are esters based on alcohols and organic acids.  They
give PVC elastic properties, so broadening its range of applications."

The manufacturers and distributors of 'vinyl' plastic tubing for the
commercial market do not specify the plasticizers used, nor do they
control the leaching of the plasticizers.  It seems that the leaching
doesn't bother their big customers.  That's bad news for us.  :-( 

For further reading visit

  http://www.cts.com/browse/hinckley/tygon.html
  http://home.t-online.de/home/Thoelen/schlauch.htm
  http://www.basf.de/basf/html/e/produkte/gebiete/ci/weich.htm
  http://www.amines.com/amines2.htm
  http://www.sdplastics.com/tygon.html

Robbie Rhodes