Why Are Invisalign Using New Materials? Mine Now Say Made in Mexico and Feel Very Different.

Invisalign started using a new material in Jan 2013.  The new material is called SmartTrack and patients have been very happy. They are easier to remove and more flexible (more comfortable).  There is nothing to worry about.
 

Invisalign has recently done a lot of research in using a new material for all the trays being fabricated from now on. It is supposed to be much more efficient at moving teeth then the old material was.

Yes, the Invisalign aligners now feel different and you are correct.  It is a different material as of January 2013.  All aligners now are made with a different material that is not as stiff but moves your teeth with a gently force with the same (if not better) movements.  

PS: They always said Made in Mexico since 1999.  They have been making them across the border in the same place that most medical manufacturers are located near Mexicali.