I have a dive buddy with a pair of OMS Slipstreams. He and I both wear DUI Rockboots size 11. I had a few conversations with others who use the same fin with Rockboots and got a recommendation to match my buddies sizes. XL Slipstreams with XL springs.

Just received a pair yesterday and put the springs on. Not sure they are going to work. Extremely tight and spring at the end of its tension.

Is there a break in period with these for the material to stretch? Very surprised at the sizing.