The first is the smooth inner surface, removing the pockets from the OE structural corrugated folds. The GrimmSpeed Hose is made with reinforced silicone, which is flexible, but has strong structural properties that allow for a design that maximizes flow, is very easy to install and won't collapse under vacuum.
The second feature is a tapered center portion, making sure the inner diameter matches the OEM air box and turbo inlet. A mis-matched diameter creates steps, which will interrupt the air flow trajectories and create small vortexes in the post-MAF hose. The GrimmSpeed Hose was designed specifically to prevent these issues.