There are several key differences between 3D and 7D mats, the most notable being that 3D mats have three layers while 7D mats have seven. The additional layers in a 7D mat provide more cushioning and support, making them ideal for high-impact activities or those with joint issues. 7D mats also tend to be heavier and bulkier than their 3D counterparts, so they may not be as suitable for travel or carrying around with you to your yoga class. Other key differences include the price (7D mats are typically more expensive) and the lifespan (7D mats usually last longer).