I bought two of these now we are working from home and have hardwood floors.  I unrolled them and weighted them with heavy books overnight and they flattened out smoothly.  They are almost invisible on the floor.  They do slip slightly, but not enough to cause a problem.  4 stars because they are still wavy, but will probably flatten out over time.  The size is just right for our desks and the mats should last a long time.