Acoustically Engineered Memory Foam
Not all memory foam is created equal: It can have a variety of densities, flexibility, air pocket ratios, and more. When memory foam is labeled acoustic, that typically means that it’s designed to dampen and channel sound (some sound rooms or performance venues put acoustic foam on the walls to help avoid echoes). Typically this is very different from the type of memory that you find in your pillow, for example. Since Apple is highlighting both the acoustic and memory features of the foam, it’s probably a memory foam material designed primarily for comfort, but with some acoustic properties to block sound from escaping or entering the headphones.