I decided to try my hand at making a flannel crib sheet for my daughters’ new baby to go with the new crib. I used this tutorial with a few modifications. It is a 70 inch piece of 45" flannel with a 9" square cut out of each corner. The corner are stitched together to form the fitted sheet. I used my serger to finish around the edges to save myself the work of hemming; the edge will be under the mattress so no one will ever know.
The elastic is applied to each corner. I used a 12" piece at each corner rather than applying it to the entire length of the sheet. Pin the middle of the elastic to the corner seam and stretch it back each way as far as you can. Pin each end. Run a zigzag stitch through the elastic.
Be sure to use an elastic that will allow you to sew through it or all your work will be for not. Some elastic will lose its stretch if you zigzag through it but this elastic worked wonderfully.
Read the application instructions on the package to determine if it can be sewn through. If it says to insert it in a casing you will not have good results if you stitch through it. I used a zigzag stitch on my machine that makes three stitches up and back rather than a straight zigzag but that would work fine too.