Manufacturer · Fashion & Home Accessories
The most suitable threads for boat upholstery and motorcycle seats are UV-stabilised polyester threads, and for the harshest marine conditions PTFE threads. They withstand direct sun, water, salt and vibration without rotting, shrinking or losing their strength quickly. Nylon and cotton threads are not suitable for exterior seams, because outdoors they age much faster.
Why boats and motorcycles are the toughest case
A car seat is behind glass and under a roof. Boat and motorcycle seats have no such protection. They are outdoors for most of their life and take several kinds of load at once:
- Direct sun – UV rays break down fibres and bleach the colour, and water and sand intensify the effect.
- Water and salt – salt crystallises between the filaments and acts as an abrasive; moisture holds dirt and leads to mildew on natural fibres.
- Heat – dark vinyl heats up strongly in the sun and the seam works at a high temperature.
- Vibration and friction – on motorcycles the seat constantly rubs against riding gear, and the edge seams take impacts.
- Cleaning – regular washing with pressure washers and detergents.
Boat upholstery thread: which material
UV-stabilised polyester
The main choice for cushions, seats and backrests on boats. Polyester does not absorb water, does not rot and, with stabilisers, lasts a long time in the sun. The bonded version sews easily on marine vinyl.
PTFE thread
For products that are never put away: bimini tops, covers, awnings, tarpaulins. The thread practically does not degrade from UV rays and salt. The price is higher, but restitching an awning is costly work, so in many cases it pays off.
Bonded polyamide
Suitable only for interior seams in the cabin or for parts that are always covered. Outdoors, polyamide loses strength faster and elongates from moisture.
Thread for motorcycle seats
A motorcycle seat is small but heavily loaded. The upholsterer works with dense vinyl or leather, often with raised seams, diamond stitching and coloured inserts. The recommendations are:
- bonded polyester thread with UV stabilisation for all visible seams;
- a thicker thread for decorative seams on the top surface – for a crisp, sporty look;
- a longer stitch on vinyl so as not to create a perforation line along which the material can tear;
- a water-resistant seam: on motorcycles water gets in through the needle holes and soaks the foam underneath, so a water-repellent membrane is often used under the cover.
Thickness, needle and stitch
| Product | Approximate thread thickness | Needle |
|---|---|---|
| Boat cushions and seats (vinyl) | tex 70–90 | 110–140, leather/vinyl point |
| Motorcycle seats – construction seams | tex 70–90 | 110–140 |
| Motorcycle seats – decorative seams | tex 135–210 | 140–180 |
| Awnings and covers (acrylic fabric) | tex 70–135 | 110–140, round point |
The needle sizes are metric (Nm) and are a guide. Choose the needle so that the thread passes freely through its eye, and make a test seam.
How to sew marine vinyl
- Use a machine with walking foot (top and bottom feed) or needle feed – vinyl sticks to the plate and the foot.
- Set the stitch length to about 4–5 mm. Stitches that are too dense weaken the vinyl.
- Do not use pins in the face side – the holes remain forever. Use clips or double-sided tape in the seam allowance.
- Keep the tension moderate: vinyl does not recover after puckering.
- Secure the ends of seams with a few backstitches, because vibration unravels loose ends.
Repair or full restitching
On an old boat often only one seam breaks, but this is usually a sign that the thread in the whole product has aged. If the material is in good condition, it is recommended to unpick and restitch all the seams in the exposed area with UV-resistant thread, using the same holes where possible. This way the vinyl is not pierced again. If the material is cracked or hardened, it is more sensible to sew a new cover – new thread will not save old vinyl.
Thread colour for outdoor products
Saturated colours such as red, orange and blue fade more visibly than white, beige, grey and black. If the client wants a contrast seam on a boat or motorcycle, choose UV-stabilised polyester and warn them that after a few seasons the shade will change. White and light grey are classics on boats, because they are the least noticeable after ageing.
You will find threads for these applications in the threads for the automotive industry range, which also covers marine and motorcycle upholstery. For leather accessories for motorcyclists see threads for footwear and leather, and for all types threads.
Maintenance that protects the seams
- Rinse with fresh water after sailing in salt water.
- Cover the seats when the boat or motorcycle is not in use.
- Do not use aggressive solvents on the seams.
- Check the seams at the start of every season – an early repair saves replacing the whole cover.
Threads for boats and motorcycles from Polkom
Polkom is a Bulgarian manufacturer of sewing accessories, based in Sofia, with over three decades of experience. We supply technical threads for marine and motorcycle upholstery, match the colour to a vinyl sample and send samples. Minimum quantities depend on the article. Write to us via Contact with the type of product and the material.
