I just received this bag which I plan to use for an upcoming trip to china. The design is very well thought out with the flexibility to have two compartments or one, backpack or wheels or duffle carry, and the expansion. The sides are not hard but are a bit firmer than I had expected -at least for the lower part of the bag.  The only thing I wish it had was a waist or chest strap for the backpack straps to help distribute the weight. I am very pleased with the bag especially for the price ($120). It has a lot more room than some of the convertible backpack i saw at REI.