A cushion cover or a sturdy fabric repair can put more strain on a seam than a lightweight garment. Coats & Clark upholstery and heavy-duty threads are options to consider, but the fabric and sewing equipment must suit the thread.
Read the thread type carefully
Extra Strong Upholstery and Dual Duty XP Heavy are different product lines. Compare their labels, fiber content and recommended uses. A stronger thread is not automatically better for every fabric: it can look bulky or cause puckering on a light material.
Prepare a realistic test
Make a sample with the same seam allowance and number of layers as the finished item. Check needle compatibility and the machine manual before using thicker thread. Inspect the top and underside of the seam, then gently pull the sample to see whether the stitches sit evenly.
Repair the fabric as well as the seam
If the cloth is fraying or thin, support it with a suitable patch before restitching. For a hand-closed cushion opening, keep stitches small and evenly spaced and secure the ends. This guide concerns household fabric projects; load-bearing equipment requires the maker’s repair instructions.
Related Coats & Clark products
Extra Strong Upholstery thread, 150 yards, black
Dual Duty XP Heavy thread, 125 yards, brown
Check the current listing for size, color and availability.