Mountain Hardwear knee articulation

Not really sure what the model name of these pants are but I found the knee construction interesting:

Rather then just have a double set of darts like most pants out there they added a whole extra circular panel to the inside of the leg, I couldn't say without holding them but it has the potential to add quite a bit of knee room to the pants. 

Also notice how the crotch gusset extends down the entire inside of the leg.