Check out this Train station in Wuhan China. The Architect, China Railway Siyuan Survey and Design Group, had chosen aluminum honeycomb panels for their absolute flatness. There are several advantages of honeycomb over ACM. One of them is that there is no Oil canning. Another one is its instant and 100% recyclability since it is made entirely out of aluminum. Hunter Douglas provided the panels. If you want to see the difference, check out the fourth picture (different project) in this post