Multi-layer exercise mat

A multi-layer exercise mat comprising:

• a first layer comprising an outer surface and an opposing inner surface, the opposing inner surface of the first layer comprising a first array of three-dimensional features integral with the first layer;
• and
• a second layer comprising an outer surface and an opposing inner surface, the opposing inner surface of the second layer comprising a second array of three-dimensional features integral with the second layer,
• wherein the first and second arrays of three-dimensional features are configured to grip each other through frictional force to removably secure the inner surface of the first layer to the inner surface of the second layer,
• wherein the first layer, the second layer, or a combination thereof has
• an Asker C hardness of 5 to 70, or
• a density of 32 to 640 kilograms per cubic meter, or
• the Asker C hardness of 5 to 70 and the density of 32 to 640 kilograms per cubic meter,
• wherein the three-dimensional features of the first array comprise projections and the three-dimensional features of the second array comprise projections,
• wherein the projections of the first array have a substantially same shape as the projections of the second array,
• wherein spaces between the projections of the first array are not a same shape as the projections of the first array, and
• wherein the projections of the second array fit between the projections of the first array and are sized to frictionally engage the projections of the first layer.