best light/packable insulated jacket (for stops, camping etc.)

Pretty much what badlywired has said..I run hot and sweat like a a sweaty thing so avoid down and synthetic for any activity above gentle walking, I tend to use base layer fleece and a windproof then add a synthetic over the top

….. Cost wise decathlon is hard to beat I have
3 year old down light decathlon jacket been excellent warmth to weight
6 month old Simond alpinist synthetic jacket….Possibly the warmest jacket I have bit bulky but is excellent
PhD down…Nice but unused for last year
Arcteryx down and synthetic mix, not that brilliant for price
Patagonia nano bad fit on me
Mountain equipment down, 20 years old refilled 18 years ago after leaking in Nepal and is the best down coat I have owned
Rab xenon okay
Rock experience bought in tk maxx synthetic for £15 rather good
Musto primaloft bought tk maxx outstanding
Finesterre survived pretty much everything I have thrown at it warm and packble
So if they fit go decathlon or luck out in tk maxx

Prism can here. I like it food not being too warm.

That decathlon number *sounds* great. If the fit is OK I’d find it hard to justify spending 3x that for something that still wasn’t expensive (relatively).