The thicker the better in my opinion. Do not butt them tight together when you lay them. Leave about a quarter to half an inch gap. If you butt them tight, they will lift from expansion during warm weather. The gap will quickly fill with debris. Some horses tend to work on the mats with their shuffling and lift the edges. The thicker mats help limit the lifting but do not prevent it. When they do, debris gets under the mat and you must pull it out, level the base and put the mat back. Having that gap helps make it easier to replace the mat. A couple of vise grip pliars will aid in moving them as a 4x6x3/4" mat weighs 100 pounds. One side of the mat will have "striations", ie; grooves at a forty five degree angle to the length of the mat. That is the bottom side. With mats, if you bed with sawdust, you can tailor the depth to the needs of the horse and cleaning is a breeze compared to dirt floors.