Measure the bottom edge of the door and add 2 inches. Cut a piece of fabric 8 inches wide and as long as the measurement you just calculated. Use any durable, solid fabric, such as denim or wool.
Fold the fabric in half lengthwise with the wrong side out. Using straight pins, pin the long edge of the folded fabric together.
Sew the fabric together along the long edge and one of the short edges using a sewing machine or needle and thread. Any simple stitch, such as a straight stitch, will do.
Turn the fabric inside out.
Fill the resulting fabric tube with insulation foam, or pack it tightly with dry beans or sand.
Hand-stitch the open end of the tube using the stitch of your choice.
Lay the “draft snake” against the gap at the bottom of the door to block breezes.