Just a quick comment. My name is Bernard Majeau and I’m the guy who designs the eBags products. If you all don’t mind, I’d like to provide an answer about cubic volume (how we measure it) and why two similar bags have different specs.

Cubic volume specs are created using a technique recognized by the American Society for Testing and Materials (ASTM). It involves filling a bag with hard plastic balls (see below) measuring ¾ of an inch in diameter. Once the bag is fully “stuffed out”, the balls are dumped into a measuring cylinder which is used to calculate their total cubic volume displacement.

We do not measure the dimensions of compartments and add them all together. I personally fill up the bag and go through the measuring process of transferring thousands of balls into the cylinder.

Regarding the differences between the two sizes, they each have unique construction techniques (where the walls are sewn, how much float there is between various compartments, the amount of padding, how many layers of fabric, etc.).

The specs for ASTM standard F2153 can be found at the following link: http://www.astm.org/SNEWS/JULY_2002/backpack_jul02.html

I hope this helps.

Regards,
Bernard Majeau
Director, Product Development - eBags