Fold fabric along the length, right sides together.
Machine or hand-stitch a 1cm seam through both layers to form a tube.
Turn tube right side out and press lightly with iron.

Turn in the two remaining raw edges by 1.5cm.
Press lightly with iron.

Slide the Sashiko pattern template centrally between the two fabric layers.

Using a water-soluble fabric marker, trace the design seen through the top layer of fabric.

Remove pattern piece. Stitch along folded edges using a blind hemming stitch.

Using Sashiko thread and long needle, sew continuous, evenly spaced running stitches 1.5cm in from edge to form a border around the mat.

Sew all the straight lines of the Sashiko design using continuous evenly spaced running stitches. For curves, use a shorter needle and work just a few stitches at a time.

When all stitching is complete, soak fabric in water to wash away the marking lines. Leave to dry. Iron to finish.