A strange thing indeed, but very simple: a synthetic quilt to cover my legs when using an insulating jacket over my torso.
The quilt was a blue pertex 4 top, black windstop lining underneath (to aid drying), and a double layer of Thinsulate sandwiched between. There were an extra few inches of pertex left as a draft excluder.
I stitched the thinsulate to the lining, then rolled the edges and stitched it to the pertex. The ‘quilting’ was a few loops of thread tied from top to bottom through all the layers. This helps stabilise the insulation and stop it shifting and tearing when being pulled out of a stuff-sack. The loft of the quilt is about an inch so the loops had to allow this expansion. I pressed an inch wide ruler into the quilt and tied the thread around it. Thread is quite difficult to tie at a specific point so this was the hardest part, although it only needs loops every foot so there were not too many. Total weight = 456g. Shame I only have access to older materials. Primaloft and lighter pertex would make it a lot more advantageous in weight terms for a full quilt and would stuff a lot smaller.
In use on the GR20 it was very good, keeping comfortable and warm even when water was pooling in the bivvy bag. I tucked it tight round me for most heat, but quilts are naturally adjusted in your sleep to get the right temperature. I ended up draping my jacket over my torso like a quilt, instead of wearing it, for this reason.
Looking back, as I never wore my base leggings, I could have used them with a full-size quilt of single thickness thinsulate. The full synth jacket was not totally necessary so I could have left it and brought my ultra-light down vest. This would have been the optimum combination for same warmth but better versatility. I may remake the quilt in this way over the winter to try out next summer. For alpine climbing, a pied d’elephant would be easy to make!
edit: NB. while researching a new bed, I have learnt that ‘quilting’ would involve more continuous lines of stitching. The stabilisation method used here is technically called ‘tufting’. There you go!