I couldn't find the right stuff locally (and didn't want to pay huge shipping cost for a roll, or wait for shipping), so I used 2 layers of 1/4" mesh (I think?) offset to give the exact same size as the varroa mesh I purchased from Dadant. It was under $10 for a 25' roll, so I can make alot of SBB's, even doubled up. Also, if you only need to make a few (and have some other stuff to order), you can buy individual sheets of plastic varroa screen from Dadant (I used one sheet to make 2 partial screened bottom boards and they are only about $2.75 each sheet.