Ultimately, Nate and I decided it's all about timing. Initially, our baby is going to be in a cradle next to our bed and isn't even going to use the crib for a few months, so we can use a crib bumper pads simply for decorative purposes during that time. Beyond that, we'll play it by ear – but we did make sure to make a crib bumper pads with thin batting so it's very breathable, just in case.
Measure the length and width of your crib (mine was 52 1/2″ long and 26 1/2″ wide). Height doesn't matter because we're going to cut all pieces to 11″ high. This height seems to be about average for a crib bumper pads.
Cut batting in the exact width and length of the crib (I cut 2 pieces of batting to 52 1/2″ x 11″ and 2 pieces of batting to 26 1/2″ x 11″).
For all four sides of the crib bumper pads, pin the batting to the corresponding fabric layers with the fabric layers on bottom. You'll notice that the batting is 1/2″ shorter than the fabric layers. This is intentional to leave a 1/2″ seam on one end, which you will slip-stitch later.
For each of the crib bumper pads' four pieces, sew three sides with 1/4″ seams. Leave open the end where the fabric is 1/2″ longer than the batting.
Turn each piece inside out.
Pin the seams together.
Slip-stitch the opposite-colored seams together.
Cut 16 strips in one of the fabric colors to 1″ x 23″. These will be the ties that attach each crib bumper pads piece to the crib.