Denim Requires Heavier Needles, Stronger Thread, and Slower Stitching Than Cotton
Sewing denim is different from sewing lighter fabrics because denim is tightly woven and thick. A standard sewing needle will bend or break when you push it through multiple layers. You need a size 16 or 18 needle (marked as 100/16 or 110/18 on the package) designed for heavy fabrics. Use heavy-duty polyester or topstitching thread instead of regular thread—it won't snap under the strain of thick fabric. Reduce your machine's stitch speed to medium or slow, and expect to sew at half the pace you would on cotton.
The most common mistake is using a regular needle and regular thread, then wondering why the needle breaks or the thread keeps snapping. Denim will punish shortcuts. If you're reinforcing seams or hemming jeans, you may need to hand-stitch the final pass because even heavy-duty machines struggle with five or six layers of folded denim.
Key Takeaways
- Use a size 16 or 18 needle and heavy-duty polyester or topstitching thread, or your needle will bend and your thread will snap.
- Reduce your machine's stitch speed to medium or slow, and expect to sew more slowly than you would on regular cotton.
- Backstitch at the start and end of every seam to lock the thread, because denim seams come undone if they are not anchored.
- When sewing multiple layers—such as hemming or reinforcing a seam—you may need to hand-stitch the final pass because the machine cannot push the needle through.
- Test your setup on a scrap of denim folded to the same thickness as your project before you sew the real garment.
Prepare Your Machine and Test on Scrap Denim First
Before you touch your project, thread your machine with heavy-duty thread and insert a size 16 or 18 needle. Check your machine's manual to confirm the needle is seated all the way in and locked. Many machines have a small lever or button that holds the needle in place—if it is not locked, the needle will shift during sewing and break.
Cut a scrap of denim at least 4 inches by 4 inches and fold it to match the thickness of your project. If you are hemming jeans, fold the scrap twice to simulate the four layers of a hem. Sew a straight line down the middle of the scrap at medium speed. The needle should move smoothly without resistance. If the needle bends, stops, or makes a grinding sound, stop when ready and check that the needle is the right size and fully locked. If you are using regular thread, switch to heavy-duty thread and try again.
Sew Straight Seams with Backstitching at Both Ends
Denim seams fail because the thread comes loose at the start or end. Always backstitch at the beginning and end of every seam. To backstitch, sew forward three or four stitches, then press the reverse button on your machine and sew backward over those same stitches, then press forward again and continue. This locks the thread so it cannot unravel.
When you sew a seam, keep the fabric edge aligned with the guide line on your machine's throat plate (usually the ¼-inch or ½-inch line, depending on your pattern). Sew at medium speed—do not rush. If the fabric bunches or the needle skips stitches, stop, raise the presser foot, and pull the fabric straight back out. Do not yank sideways, or you will bend the needle. Reposition and start again.
If you are sewing a seam that crosses a thick area—such as where two inseams meet on jeans—slow down even more. You may feel the needle hesitate as it pushes through. This is normal. If the needle stops completely and will not move, raise the presser foot, back the needle out, and hand-walk the needle through by turning the handwheel on the side of the machine one stitch at a time.
Reinforce Seams on Stress Points Like Crotch and Inseams
Jeans fail first at the crotch seam and the inseams because these areas take the most strain. Reinforce them by sewing a second line of stitches parallel to the original seam, about ¼ inch away. Backstitch at both ends. Some sewers sew a box pattern—a rectangle around the original seam—for extra strength.
When you sew over an existing seam, the presser foot may rock because one side is thicker than the other. Slip a thin piece of cardboard or a seam ripper under the presser foot on the thin side to level it. This keeps the needle from bending and the fabric from bunching. Remove the cardboard after you pass the thick spot.
Hem Denim Without Breaking Your Needle
A denim hem is usually four layers thick—the original hem folded up, then folded again. This is too thick for most machines to sew in one pass. Instead, sew the first three layers with your machine, then hand-stitch the final fold.
Fold the hem up to the length you want and press it flat with an iron. Fold it up again ½ inch and press. Pin it in place. Thread your machine with heavy-duty thread and a size 16 or 18 needle. Sew along the crease of the first fold, backstitching at both ends. The needle will push through three layers. Stop before you reach the final fold—do not try to sew through all four layers at once.
For the final fold, thread a hand-sewing needle with heavy-duty thread and knot the end. Bring the needle up through the fold from inside the pant leg so the knot stays hidden. Take small stitches (about ⅛ inch) along the crease, catching only a thread or two of the outer fabric so the stitches do not show on the outside. When you reach the end, take two stitches in the same spot and knot off.
Patch Denim by Sewing a Reinforcement Patch Underneath
A patch sewn on top of denim is visible and looks temporary. A stronger repair is to sew a patch underneath the hole. Cut a patch from denim scraps at least 1 inch larger than the hole on all sides. Position the patch under the hole and pin it in place from the inside. Sew around the patch ¼ inch from the edge, backstitching at the start and end. Use a size 16 or 18 needle and heavy-duty thread.
If the hole is large or the fabric is torn, trim the torn edges straight before you explore the patch. Fray the edges slightly by rubbing them with a wire brush—this helps the patch bond to the fabric. Sew the patch on, then sew a second line of stitches ½ inch from the first line for extra strength.
Avoid Common Mistakes That Break Needles and Snap Thread
The most common mistakes are using a regular needle, using regular thread, sewing too fast, and not backstitching. Each one will cause failure. A regular needle bends when it hits thick denim. Regular thread snaps under the strain. Sewing too fast makes the needle skip stitches or bend. Not backstitching means the seam comes undone the first time the garment is worn.
Another mistake is sewing over pins. Denim is hard enough that hitting a pin can break the needle. Remove all pins before you sew, or sew slowly and stop before you reach each pin, remove it, and continue. Do not sew backward over an existing seam without slowing down—the needle can bend if it hits the old thread at an angle.
If your thread keeps snapping, the problem is usually tension. Check your manual for how to adjust the tension dial on your machine. Denim often needs slightly looser tension than cotton. If you are not sure, sew a test line on your scrap and look at the underside. If the top thread is pulled tight and the bottom thread is loose, tighten the top tension slightly. If the bottom thread is pulled tight, loosen the top tension.
Frequently Asked Questions
Can I use a regular needle if I sew slowly?
No. A regular needle will bend or break no matter how slowly you sew, because denim is too hard. You need a size 16 or 18 needle designed for heavy fabrics. The size number tells you the needle is thicker and stronger.
What do I do if my needle keeps breaking?
Stop and check three things: the needle size (it should be 16 or 18), whether the needle is fully locked in the machine, and whether you are sewing too fast. If all three are correct, the problem is likely tension. Loosen the top tension slightly and test on a scrap. If the needle still breaks, you may have a bent needle in the machine—remove it and insert a fresh one.
Can I use regular thread if I sew carefully?
No. Regular thread will snap under the strain of denim, even if you sew slowly and carefully. Use heavy-duty polyester thread or topstitching thread. These are thicker and stronger and designed for thick fabrics.
How do I sew through the crotch seam where four seams meet?
Slow down to a crawl and hand-walk the needle through by turning the handwheel on the side of the machine one stitch at a time. You will feel resistance—this is normal. If the needle stops completely and will not move, raise the presser foot and try again. If it still will not move, you may need to hand-stitch this section with a needle and thread instead.
Do I need a special presser foot for denim?
No, but a walking foot (also called an even-feed foot) helps keep thick fabric from bunching. If you do not have one, you can level the presser foot by slipping a thin piece of cardboard under the thin side when you sew over a thick seam.