The origin of the portage pack goes back to the days of ancient history even before front suspension when it was the norm to carry your bike over technical terrain instead of riding it, amazing. These days it's still a handy place to stash gear, mounting under the top tube and in front of the seat tube. Or, if you live on the third floor without an elevator it helps too. Most competitors designs have either a PVC or Aluminum stiffener, both of which are not very adjustable and can break when used on the wrong frame geometry. The Inertia Portage Pack uses a semi rigid HDPE stiffener so it can flex and fit a wider range of bikes, we also throw in 3M Scotchlite Reflective Material on both sides of the bag for added safety.