While not a true solid 3" height due to the convoluted top, it was plenty wide and long and fit my mattress edge to edge.  I use the ridges up towards our bodies, although since it is buried under the fitted bottom sheet and the thick mattress pad, I am not sure how much air flow it provides.  But, It is NOT hot though like other memory foam pads I have used and you do not sink excessively deep into it either to where you would struggle to move or roll over.  A nice compromise, and a great value to make my old mattress more comfortable.  Again, fast free delivery from Wayfair: always my go to venue when I need something for the house!