Patching a worn knee from the inside

Trousers can be patched from the inside so the repair is mostly hidden from the outside. A fabric patch is cut larger than the worn area, placed behind it and stitched to the trousers, so the knee keeps its shape while the stitching stays fine and close in color to the fabric. The approach works well on cotton, denim and wool trousers, provided the fabric beneath the knee is still strong enough to hold stitches and the patch matches the garment in weight and fiber content.

Assessing the knee before you start

Turn the trousers inside out and lay them flat on a table. Look closely at the worn area. If the fibers are crumbling, or if the fabric has thinned to the point that a needle pulls through without much resistance, a patch will not have enough to grip. In that case, the garment may need a tailor or a replacement rather than a patch. A knee that is only thinned, with threads still intact, is a good candidate for an inside patch.

Note the location of seams and any pockets, because a patch placed over a seam is harder to stitch and may stiffen the garment. Check whether the trousers are lined in the knee area, which is uncommon in casual trousers. If they are, work between the lining and the outer fabric through an opened hem, or take the trousers to a tailor. The patch sits on the inside, so the choice of fabric is about comfort and durability rather than appearance. It should be close to the garment in weight and fiber, as explained in the next section.

Choosing and cutting the patch

Use a fabric that matches the trousers as closely as possible. Scraps from the hem or a spare piece of the same fabric are ideal. Denim patches suit jeans, and a medium-weight cotton twill works for chinos. For wool trousers, a lightweight wool or wool blend scrap is best. If the trousers will be washed, pre-wash the patch fabric too, so that it does not shrink differently and pull the knee out of shape afterward.

Cut the patch with rounded corners, which lie flatter and are less likely to lift. Make it about 1 1/4 to 1 1/2 inches larger than the worn area on every side. The extra fabric gives the stitches enough material to hold without sitting too close to the damage. Press the patch flat, then position it inside the trousers behind the worn section. Align the grain of the patch with the grain of the trousers, so the lengthwise threads run in the same direction. Mismatched grain can make the knee pull to one side. Hold the patch in place with pins or a light basting stitch around the edges.

Because the knee bends more than most other parts of the leg, a patch can be slightly lighter than the trousers, but never much lighter. A much lighter fabric tears at its edges under repeated bending, and a heavier one makes the knee stiff and uncomfortable when sitting or crouching.

Stitching the patch from the inside

Stitch around the edge of the patch with thread that matches the trousers. Hand sewing with a small whipstitch or a backstitch is a sound option, and a sewing machine with a narrow zigzag or a short straight stitch works well on flat areas. Reaching the knee on a machine depends on the leg width. On wide legs, slide the leg over the free arm, the narrow part of the machine with nothing beneath it, so the knee sits under the needle. On slim legs the leg will not fit over the arm, so open the inseam far enough to lay the knee flat, stitch the patch, and resew the inseam with matching thread. If you would rather not open a seam, hand stitching is the practical route. Keep the stitches close to the patch edge and small enough to hold the fabric.

Be realistic about visibility. A machine stitch always goes through to the right side, and so does any reinforcing line of stitching. A hand stitch can catch only part of the thickness on heavier cloth such as denim or wool, so it may not go through at all. Machine and reinforcing stitches show as fine lines on the outside, which matching the thread color keeps subtle.

Stitch the worn area too, not just the edges. Work short rows back and forth across the thinned fabric, passing through the worn cloth and into the patch on every row, with the rows about 1/4 inch apart. This ties the worn fabric to the patch so the two layers wear as one. On a heavier-wear knee, these rows also spread strain more evenly, so the patch does not tear along a single stitch line. Without them, the thinned fabric keeps abrading and can open into a new hole over the patch.

Start and finish each line of stitching with a few small backstitches so the thread cannot loosen. Loose ends inside the leg can snag on skin or work their way out of the seam, so tidy them while the trousers are still flat on the table.

Work slowly and check the outside as you go. If a hand stitch shows through to the front, unpick it and try again with a shallower entry. Keep the fabric flat under the presser foot or on the table, and avoid stretching the knee while sewing. Once the patch is secure, trim any loose thread ends and press the knee lightly from the inside to set the stitches.

Caring for the repair afterward

The knee takes more movement than almost any other part of trousers, so the edges of the patch will see the most stress. Wear the trousers for a few days and then check the stitching. If any part has come loose, restitch it before the gap spreads. Wash the trousers inside out on a gentle cycle and avoid high heat when drying, since heat can shrink the patch differently from the surrounding fabric and cause puckering.

A patch can extend the life of trousers that have worn thin in one area, but it does not restore the original strength of the whole garment. If the fabric beside the patch starts to thin, or if new wear appears at the edge, a second patch or a decision to retire the trousers may be the practical next step.