How to bond a TPU 3D-printed part to fabric

TPU is a thermoplastic elastomer, which means it is flexible, chemically fairly resistant and low in surface energy. That combination makes it awkward to bond. Most rigid adhesives either will not wet it or make a hard spot that defeats the point of using a flexible material. A flexible contact adhesive, of the sort used in shoe repair, is the right family.

Fabric brings the opposite problem: it is porous, so adhesive soaks in and stiffens the weave. Applied thinly that is a small penalty, applied thickly it turns a soft textile into a board. Two thin coats work better than one heavy one, and the second coat is mostly there because the first one soaks in.

Printed TPU has a layered surface which actually helps the mechanical key once it is lightly abraded. Keep the abrasion light, because TPU tears easily if you dig into it.

For anything that will be laundered, treat adhesive as a backup. Repeated wash cycles with heat and detergent will work at any adhesive bond to a textile, and stitching is what keeps it together.

1. Abrade the bonding face of the TPU print lightly with 220 grit, just enough to dull it.
2. Wipe the TPU with isopropyl alcohol and let it dry.
3. Make sure the fabric is clean, dry and free of any fabric softener residue.
4. Brush a thin coat of flexible contact adhesive onto the fabric and let it soak in, then add a second thin coat.
5. Brush one thin coat onto the TPU.
6. Wait until both faces are touch dry, usually 10 to 15 minutes.
7. Press the two together firmly, working from one edge, and roll the joint down.
8. If the joint takes load or will be washed, stitch round it once the adhesive has set.