It is knit in aran-weight yarn. The main section is knit in Fisherman's ribbing, resulting in a very stretchy, cushy fabric that will stretch to accommodate growing baby. The moss stitch button bands offer some structure for holding it in place over a coat.
The pattern also includes instructions for fixing the blanket directly to the carrier, so that it can be used with a zipped jacket, or an extra weather proof layer, or for back carries.
download on Ravelry here. One step closer to ensuring my child is covered by wool at all times!
EDIT: because I am a little forgetful & didn't think to mention the yarn the first time!
I used 4 balls of King Cole Merino Blend Aran for this project with just a couple of grammes left over.