63d2328e_rication___Australian_Robotics__Sources
[Description] Generic Household Sponges [3] Supermarkets and elsewhere [Sources] 
Used during the etching process - just cheap and cheerful normal ones that I usually end up cutting into a further 4 sponges each
PC to PCB in under 30 minutes - Quick 'n Easy PCB Fabrication | Australian Robotics
Sources