HDO/H₂O (lower points) and D₂O/HDO (two top points) abundance ratios measured for warm gas in low-mass protostellar regions and in comets (JFC = Jupiter Family Comets; OCC = Oort Cloud Comets). The HDO/H₂O data are taken from the summary in Jensen et al. (2019) (brown: isolated protostars; blue: protostars in clustered regions), the D₂O/HDO star-formingcloud ratio from Coutens et al. (2014) and the HDO/H₂O and D₂O/HDO ratios in comet 67P (JFC high points) from Altwegg et al. (2017). The much higher HDO/H₂O ratios found in the top layers of multilayer ice models are indicated with the light green zone and are similar to the HDO/H₂O values of 0.025 measured with Herschel-HIFI in cold outer envelope gas.