It's called "chiropody sponge". Horos is the brand I think. I still have cracks but was told with using this and the cream it would still take about 6 weeks for them to be fully healed. They looks heaps better though and after the first use of the sponge I was amazed. Just don't scrub hard or for too long.

The chemist lady told me to use it abut 2-3 times a week to begin with then once or twice once my feet were healed.