After having these for a while now, I am not really happy with them. They are supposed to be washable but the ivory now just looks grubby even straight out of the washer, and the tacky backside is no longer tacky. I only have 3 steps to put them on so alternate a set allows them to be alternated with one spare. They are used on the entrance steps to my motorhome. 
On the right of the photo is the unused one. On the left is one straight out of the washer