To each of the different sizes squares, I applied a thin black cotton material as the sponges were made up of multiple colours which wouldn’t have matched the layout and colour schemes of the box.
Applying cotton over the sponges didn’t make a difference to the amount of water added because that itself has a good water intake. I trying testing these on the boxes, sticking them down with masking tape to see how they would fit and if the lid of the box would fit correctly. It worked.
To glue these down I will apply UHU glue to the edge of the sponge as well as apply duck tape to keep the secure as possible.
They can now be glued to the box