(Quoted from Kieth Stevens & International Coatings. Full article here.)
In Part 1 of this article, Kieth Stevens discussed the importance of using the right tool for the job, specifically some attributes about squeegees, such as durometer/hardness.  If you missed the post, you can read it here.
To see the entire article as published in Specialist Printing Worldwide, Issue One 2015, you can read the PDF here.
Part 2:
SQUEEGEES – Continued
Composite Blades
As I mentioned in Part 1, some squeegees are composed of a “sandwich” of different durometer blades.  This type of squeegee blade consists of dual or triple blades of varying durometers sandwiched together, such as a 60/90 or a 70/90/70. The benefit to using this type is that the harder durometer gives the squeegee great support, yet has the softer edge for printing.
The disadvantage of the multi durometer i.e. 60/90 is that since only the side with the soft edge is used for printing, over time, the squeegee will curl to one direction.  Hence the invention of the triple blade, where both sides of the blade can be used for printing and can therefore be balanced and kept straight.
Due to harsh cleaning chemicals and age, squeegees over time will become harder in durometer or even become brittle. So keep that in mind and when you think it’s time, go ahead and get a new blade. You may be surprised at the difference a new blade can make.

Click here to read the full article