How to insulate this wall?

[mindthatwhatouch]

Take a look at R values. Higher number is more insulating. PIR is better insulator than Glass wool or polystyrene.
You maybe able to find some excess boards from a nearby build to keep cost down?

 

[throbscottle]

Hadn't heard of R values - but it is thermal resistance, which I do understand!
Garage door is pretty un-gappy - certainly no howling gale there. It would stand also being insulated though.
@bignik - I think the problem would be volume. It's quite a lot of stuff to find.

Well, looks like Superfoil or PIR is the way to go. Or.... get saving up bulky stuff!

 

[MikeJhn]

The only thing the multi layer foil is good for is to hold in place the real insulation you put up, the whole point of insulation is to create still air.