Yes, I think so. The sides under the arms are high perspiration and heat areas that are best ventilated at the source and the side mesh panels do just that. Also since those areas are covered by your arms they do not have to be as waterproof I guess (though that part of the Atom is still water repellent regardless). The jacket is popular among active climbers and here is a review I found by one: http://www.mountaingear.com/themount...-jacket-a-lot/

Also, I am referring to the LT version, not the AR which is a heavier jacket.