Most of these models have breast implants. You get "360 cleavage" when you have a bag of silicone or saline behind your actual breast. You can tell when there is a very distinct "line" or the model has side or bottom cleavage when lying down with no support. As many implants encapsulate (a hard coat of scar tissue forms around the implant) it makes the breast look and feel even more firm, hard actually. These breasts rarely even move when the model jumps, and the "360 Cleavage" and the heavy "lines" which then look like ridges are even more pronounced.

It's a nearly impossible look to achieve with natural breasts. That's one reason that push up bras are so popular; you can take them off and there's no anesthesia involved. less