any given time. As a result defining which gas has been evaporated is not entirely clear cut.

We have tried a variety of approaches for determining the effective evaporation timescale for our simulated remnants. One approach is to use a density criterion to decide what is cloud material and what is evaporated. In our case we defined the mass in clouds as the mass of gas with density above a 2.5 cm$^{-3}$, which is the geometric mean of the density of intercloud medium, 0.25 [cm$^{-3}$]{}, and the cloud density, 25 [cm$^{-3}$]{}. The mass of gas evaporated from clouds at any given point in the remnant’s evolution is then the mass that was in clouds initially within the shock volume minus the mass in clouds at the current time. The average evaporation rate is then the evaporated mass divided by the remnant age. Connecting this evaporation rate to that predicted in the WL model is not entirely straightforward however, since they did not tally that quantity. Instead we can connect the intercloud mass, that is all the mass inside the shock that is not in a cloud, with the total integrated mass in the WL model since the density, $\rho$, or 