Firstly, it is Nalgene tubing, which is a specific formulation of PVC, just as Tygon is a specific formulation of something-or-other (for the life of me, I cannot find the chemical makeup of Tygon listed anywhere). I think it is fairly obvious that these (Nalgene, Tygon) are competing products made by different companies. If you read the published specs, in terms of chemical resistance and physical properties, it is equal to Tygon. Specifically, the stretch (% elongation) is identical for both (450), and so is the shore hardness (55) and operating pressure (30 psi at 73F for Clearflex60 vs 25 psi at 73F for Tygon). Chemical resistance is a bit trickier, but both claim to be non-aging and resistant to many chemicals. If you want to verify this for yourself, take a look at the following urls:
http://www.fabcoplastics.com/catalog/section7/7-008.pdf
http://www.flextubing.com/SelectionGuide.htm
http://www.tygon.com/pdfs/tygr3603.pdf
I cannot comment on memory, since the stuff has not arrived yet. However, unless someone can point out something I am missing, Clearflex60 is a good substitute, especially considering the price of Tygon. I will let you know what my impression is when I get the stuff in a couple of weeks.