Left: Upper limits for the dust-to-gas ratio A_V/N_HI against redshift, for the subsample of DLAs with N_HI > 10²¹ cm⁻². Here, A_V are derived from the assumed reddening of the β_UV slope, and so are taken to be upper limits. The majority of the sample are consistent with being dust-poor, lying below 10% solar metallicity. Right: The trend of A_V/N_HI against gas-phase metallicity 12+log(O/H), compared to values from the Milky Way, Large and Small Magellanic Clouds, and 10%, 5%, and 1% metallicities (metallicity for each represented with a star). The black line shows the relation for local galaxies and gamma-ray bursts (GRBs) (Heintz et al. 2023b). The method for calculating metallicity for each object is represented by different symbols; each still represents an upper limit in A_V/N_HI, and is colour-coded with lensing-corrected UV magnitude.