Hi There, You can also make one from 'core flute'. It is what they make the lightweight signs from. Bunnings do have some black core flute in small sheets simply cut to size, look in the 'wood' section , why it's there I have no idea
, cut the sheet to the size required and then slice the channels on the outside of your shield, fold into your round shield and then using some tape you can then tape it together. Also at the end it will lay flat so less of a storage problem..