Finished this single thickness. Picked up stitches along the start edge (I should have used a provisional cast-on) and am about half way through the second half by knitting as if starting the first. Will fold one half inside the other along the ‘start’ edge to make the double thickness. I feel it needs double thickness given the non-wool yarn used to make it warmer.

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Am hoping to modify this to make it double-thickness. May pick up another 144 st along the start edge and knit another whole hat, in effect, before folding it double along that start edge. Or I might leave it single thickness. Dunno yet.