I always wear the double layer Rainbow Sandals. The "layers" are memory foam.
Here is the deal. When you buy Rainbow Sandals, you get a FLAT footbed. YOU get to make the foot mold by wearing the sandal. Your weight, the heat of your foot, activates the memory foam and a mold begins to form. The impression of your foot is molded into the footbed. The double layer of memory foam supports heavier weights for a longer "lifetime" of the sandal. This sandal as well as the single layer has a "lifetime warranty". You will be able to walk your foot through the bottom on the sole before any strap or glue delam happens. Custom made.