Felt Blackboard Eraser. This small felt block is perfect for cleaning quickly or correcting during lessons - without water or chalk dust. The felt block has deep ribs, which absorb the dust. The slightly rough surface gives the necessary resistance to remove chalk easily from the blackboard. Cleaning the felt block is easy: just beat out the chalk. Never clean the felt block with water. Felt Blackboard Eraser. 12.7x5x3.5 cm (5x1.97x1.38 inch).