We don’t know exactly what process causes this phenomena but with any bulk order some playmats (shipped straight from the manufacturer) would arrive with odd discolorations, skuffs or markings on the back (non-skid) side. No amount of Windex or prayer seems to remove this. Despite its pristine frontside (because of the minute, skuffed-up, rubber, side) the playmat was removed from the “perfect condition” versions, which were sold in the store. Now that the “Hanna” playmats are long out of stock and still regularly sought after we figured it’d make a great auction candidate.