Solder sponge 40mm x 55mm
As you solder you will often see your soldering iron tip starts building up a blackish material, you need to clean it off as often as you can to ensure proper soldering joints.
This yellow solder sponge is used for removing solder residue from your soldering iron tip while soldering and to clean it before and after soldering. You can also use it to keep PCBs and components clean.
To use it you need to wet the sponge and squeeze out the water from the sponge so it is still slightly wet but not dripping water.