I use 4 x 8 foot black stall mats, they are heavy, but these are about 3/8s inch thick and have a slight rib on one side and a bubble rise on the other. I take them out and wash them in good weather and just clean in place in bad. I love them, my old knees appreciate the bit of give when I need to get down and it helps me with a insulator between the frozen ground and the not frozen feet of my birds. I think the reference to 'heavy' mats is directed toward the 3/4 inch solid ones, I have one in the back of my truck, they are very heavy.
Best to you and your birds,
RJ