This is a brand new foam seal gasket for the cyclone on late cylinder ball models such as: DC28c, DC33c, DC37, DC39.
This is the gasket seal that is accessed by splitting the cyclone. Sometimes these degrade and cause cyclone leakage and thus suction loss.
Sometimes when you split a cyclone for cleaning, the old one is unusable rendering the cyclone effectively scrap. However, you may now purchase the replacement cyclone gasket seals here. Image result for dyson dc37 gasket
Please note this part is a non genuine compatible spare part and the manufacturers' names and part numbers have been used for reference purposes only