Thermal blinds or plugs for skylights?

[Garald]

How would one go about improving the thermal insulation of skylights in winter nights?

- One can get pleated blinds from the manufacturer - that's the easiest option, but their added R is relatively piddling (in the order of 0.25 m^2 K/W).
- In principle, one could imagine some sort of thick, insulated plug to put in the skylights, but I have no idea of how to keep such a thing in place.
- An intermediate (still DIY) option would be to have a kind of shade with a serious amount of wool insulation (several cm) or else the stuffing that goes into sleeping bags - while I'm about to do that for a metal door, I have no idea of how this would work in practice for a skylight. Surely something like this has been tried?

I've seen listings online for insulator pillows for RV skylights - why does there seem to be no such thing for residential skylights? Would a foam pillow just not be stable in a larger skylight (say, 78x98)?

Edited Sunday at 21:34 by Garald

[SteamyTea]

Try my secondary glazing idea that I suggested for your main windows a while back.