Thank you Tartan! I am backing with flannel - in the hopes it will be cozy and shrink at a similar rate. I called Moda customer service a week ago and they confirmed that 1/4" seam would be ok with the charm packs. I may use 3/8" on the backing since that was 'cut straight' as opposed to the 'teeth' of the charm square cut. Thank you for the great info on the poly batting too!