Mulch should FEED the soil! Un-decomposed organic matter, rock, plastic, rubber...do nothing for your soil. Your plants NEED a live, thriving, communal soil or they won't thrive. Healthy soils have micro and macro organisms (the more the better) that need to be fed. These critters eat decomposed organic material on the soil and digest it then poop it out in your soil profile. This activity mixes organic material into your beds and aerating at the same time. They also work with the plant roots to help plants uptake the nutrients they need to make their own food and be vigorous.
These important soil organisms go to sleep if all there is is non-decomposed bark, wood chips, straw on top of the soil. The decomposers get busy of course but they need a lot of nitrogen for their fuel to do the decomposing. Making less available for use by plants.
I remember researching this rubber mulch (for a play lot) and found this material was FLAMMABLE. Maybe that has changed...but not a good solution for plants.
If you need mulch for ornamental plant beds, not vegetables, the BEST mulch in my opinion is Gro-Co. Human poo mixed with sawdust and completely decomposed. It is tested by law, you can get test results, there are no WEED-SEEDS, no PESTICIDE RESIDUE. 2" smothers existing weeds and weed seed and looks gorgeous. A natural dark taupe, no rocks, no sticks, a very fine texture and...it smells NOTHING like what it came from...honest. You have to check in your own city for who makes this product. Gro-Co was just the name of this product in the Seattle, Washington area. This stuff looks great, your plants will actually look better in one week (no kidding), it is better at weed suppression than bark, plastic...yet it also feeds your soil which helps your plants function with vigor in making their own food. Kinda kills 3 birds with one stone? Grin. Hope this helps...