To clean just wipe with a soap and cold water and leave to air dry.
They should last about a year and at the end of this time can be composted or cut into strips and used as firelighters.
If needed you can refresh them by redistributing the wax. Simply pop them flat on some greaseproof paper and put them in the oven (100 degrees Celsius) for 6 minutes.
1 x Large 35cm x 35cm / 1 x Medium 25cm x 25cm / 1 x Small 20cm x 18cm