iPhone 6s Design
This is an "s" release for the new iPhone, so don't expect massive changes to the iPhone 6s design. It will not be the same iPhone though, as rumors show two major iPhone 6s design changes.
9to5Mac reports that Apple will announce a new Rose Gold iPhone 6s color option. This will match the look of the Rose Gold Apple Watch Edition, but will be aluminum instead of gold. There is a good chance that this will be hard to find in stock right after the iPhone 6s release date.
We also learned from a video on UnboxTherapy that the iPhone 6s design will use a new stronger Series 7000 aluminum that should prevent bending that plagued some iPhone 6 and iPhone 6 Plus owners.
Samsung uses this in the Galaxy Note 5 and it is commonly found in aerospace applications.