The question ‘Are supernovae important sources of dust?’ is a contentious one. Observations with the Infrared Astronomical Satellite (IRAS) and the Infrared Space Observatory (ISO) only detected very small amounts of hot dust in supernova remnants. Here, we review observations of two young Galactic remnants with the Submillimetre Common User Bolometer Array (SCUBA), which imply that large quantities of dust are produced by supernovae. The association of dust with the Cassiopeia A remnant is in question owing to the contamination of foreground material. In this paper, we compare the emission from cold dust with CO emission towards Kepler’s supernova remnant. We detect very little CO at the location of the submillimetre peaks. A comparison of masses from the CO and the dust clouds are made, and we estimate the 3σ upper limit on the gas-to-dust ratios to be in the range 20–60. These results suggest that we cannot yet rule out freshly-formed or swept-up circumstellar dust in Kepler’s supernova remnant.