I took a sample hammer each of Renner Premium Blue (Weickert felt), Abel "Special" (PIanotek), and Ronsen Weickert Special Low Profile, and cut down the center of the molding. The molding opened up due to the tension of the felt (I did nothing to open them, just cut the wood and recorded what they looked like). I also did some older hammers for comparison: Tokiwa from the 80s, Steinway from the 60s, Abel from the 90s, used hammers. They opened much less.