Yes! Many outdoor suppliers these days are offering backpacking sleeping bags with tighter nylon weaves or specialty spray-on coatings that increase the water repulsion properties of the exterior. While this can be a handy feature for those camping in inclement weather conditions, it can also lead to a bag that is less breathable (and therefore less comfortable). Remember that a sleeping bag is mostly designed to keep you warm, while the tent is what has been designed to keep you dry.