Material pair

Fabric to Leather

Best bet

Flexible fabric adhesive

Stays soft once cured, so the seam can still bend and fold.

Preparation

Prep each side differently

Trim frayed edges and wash out fabric-softener residue.

Lightly rough up glossy finished leather so the adhesive can grip.

Conditions

Seams under real tension (straps, belts) want stitching with adhesive as backup. Suede and unfinished leather grip better than glossy finishes.