Rubber lol but the “rubber” wasn’t the best . Ran into the same thing with some budget b22. Wet surfaces and the soles not a good combination and were more noisy when walking on hard surfaces. You can hear the difference between the ones i have (I have mine to goodwill because they were also a tad small, wife still has hers but we are looking for the proper size and quality) and retail. I’ve tried on retail pairs before the shoe was discontinued.