Taking a page from the Motocrossers, the grip has an inverted ridge near the flange. The MX'ers started running these on their grips so that they could use thin gauge wire and secure the grip onto the bars tightly. It also serves to keep water out saving us bmx'ers from a case of the throttle grip. On the inside of the flange side of the grip are another 4 small ridges. I can only assume these are to help keep the grip even more firmly onto the bar and to reduce any slippage during operation.
The rubber of the grip is made of a soft compound - they feel soft but definitely not too spongy. I ride with gloves but these grips have so much traction on them I could easily ride without them. Plastic bar ends compliment each grip.
Chris has gone with a smaller flange on them along with a pair being in the $10 range. Their price is a little higher than your average grip but there is nothing average about this grip from the very detailed design down to the high quality packaging.