if your blocks are quite large you might want the X just so when it's washed/dried they do not 'puff' become pillowy...but if the blocks are fairly small (less than 10" I would guess) it will be fine without the X. I only say this because the kids one time made one with 12" squares- it was very cute- but the 3 layers did not really shrink equally (cotton, muslin, flannel, flannel== I don't know why they chose to include the muslin) they did not think they needed to stitch the sandwiches- since no batting to pull apart- but it came out rather puffy & wonky in places- still good for what it was for- (a play blanket) but I think the larger the squares the more 'stability' the layers need.