Just realised the honeycomb blinds looks to be the way to go.
This appears to be a good comparative test for a few options:
So reflective roller blind actually beats the honeycomb blinds, so I guess optimal would be honeycomb with reflective outside. I see that there is cellular blinds with a 'reflective mylar coating":
Has anyone come across this in Australia or someone that ships here?
Anyone bought these and can recommend or not?:
Note that my main window areal to be covered is south facing so was going to go non blockout blinds there so I guess that can't be combined with reflective outside. Going white appears best though. Any thoughts?