A rear window louvre or a tailgate spoiler is bought for looks, but it is judged on two things that have nothing to do with looks: whether it stays on the car at motorway speed, and whether the driver can still see out of the back. Both are decided long before production, by the material, the mounting method and the tailgate details you give the factory.
This guide is for accessory wholesalers, retailers, online sellers and companies building their own brand. It covers how louvres and spoilers are made, what to send a factory so the part fits, how to specify the mounting and the tests behind it, paint and finish, and how to check the rules in the market where you sell. For the wider picture on buying car accessories from these three countries, including importer liability, see our car accessory OEM guide for Taiwan, Thailand and Malaysia.
💬 Looking for louvres or spoilers for the models you sell? Send us your model list and we will find factories in Taiwan, Thailand and Malaysia that already make the part. Ask about car accessories OEM.
Louvres and spoilers come from different production lines
A louvre and a spoiler look like neighbours in a catalogue, but they are often made by different processes, so ask each factory which process it runs before comparing quotes.
A rear window louvre is a slatted cover that sits over the rear glass. A rear spoiler sits on the roof edge above the rear glass or on the boot lid. Both are shaped for one vehicle, and both are exposed to sun, rain, car washes and air pressure at speed.
The common material and process routes are below. A factory strong in one is not automatically strong in the others.
| Material and process | Typical use | Strengths | Watch for |
|---|---|---|---|
| ABS, injection moulded | Louvres, small spoilers | Repeatable shape, takes paint well | Needs a steel mould per model; heat and UV resistance depend on grade and paint |
| ABS, blow moulded (hollow) | Larger spoilers | Light, stiff hollow section | Wall thickness varies; check for thin spots at corners |
| Polyurethane (reaction-moulded) | Lip and boot spoilers | Flexible, tolerates small panel variations | Surface needs careful priming before paint |
| Glass-fibre composite | Low-volume and custom spoilers | Low tooling cost | More hand work, so finish varies piece to piece |
| Carbon-fibre composite | Premium spoilers | Light, distinctive look | Clear-coat yellowing and resin quality need proof |
| Aluminium slats | Some louvres | Rigid, does not warp | Edges and fixings need finishing; corrosion at joints |
When you ask for quotations, name the material, the grade and the process. “ABS spoiler” alone lets one factory quote injection moulding and another quote vacuum-formed sheet, and the two are not the same product.
Fitment starts at the tailgate, not the catalogue
Give the factory the model code, years and body type, and list every item on the tailgate that the part must clear.
The same model name can have a different tailgate in a different market or after a facelift. A louvre or spoiler that fits one version may foul the other. The things that most often cause a misfit are:
- the rear wiper and its arm sweep
- the high-mounted stop lamp, which a spoiler may need to surround or leave clear
- a rear camera or sensors near the tailgate edge
- heating lines or an antenna printed on the rear glass, which a clip or tape must not damage
- the gap between the tailgate and the roof when the tailgate opens
A spoiler also adds weight to a tailgate: check that it still stays open on its struts and closes without the spoiler touching the roof. Ask which vehicles the factory has actually test-fitted, and in which market specification.
Mounting: the part that decides safety
The main safety risk with louvres and spoilers is detachment, so the mounting method and the tests behind it are the specification that matters most.
There are three common methods, and many products combine them:
- Double-sided tape: no drilling, quick to fit, but only as good as the tape grade, the surface preparation and the fitter
- Clips or brackets: louvres often hook under the rear glass seal or clamp at the tailgate edge; some are hinged so the louvre can be lifted to clean the glass
- Bolts through the panel: the strongest hold for larger spoilers, but it means drilling the tailgate and sealing the holes against water
For tape, ask for the tape maker’s grade and its temperature range, and whether a primer or adhesion promoter is part of the kit. For bolts, ask for the fastener material, the sealing method and the drilling template.
Then agree the tests in writing. The factory may have its own procedures; what matters is that the test, the sample and the pass criteria are written down before you approve volume.
| Test to agree | Why it matters | Evidence to ask for |
|---|---|---|
| Adhesion after heat and cold cycling | Tape bonds weaken after summer heat and winter cold | Test method, conditions and photos of the failed and passed samples |
| Pull or peel test on the fitted part | Shows how much force the mounting holds before it lets go | Test fixture, force applied and the failure point |
| Weathering of plastic and paint | Fading, chalking and cracking create returns | Report to a named method, for example ISO 4892-2 (xenon-arc exposure of plastics), with the exposure conditions stated |
| Road and car-wash trial | Real airflow and brushes find weaknesses lab tests miss | Your own trial on a vehicle, with the sample fitted by the instructions you will ship |
| Water test for drilled fixings | A leak into the tailgate is a warranty claim | Sealing method and a hose or spray test on a fitted sample |
ISO 4892-2:2013 describes how to expose plastics to xenon-arc light with moisture to reproduce real-use weathering. Naming a method does not set the pass level; agree the exposure hours and the change in colour or surface you accept.
💬 Want a sample fitted and checked on a real vehicle before you commit? We arrange samples, agree the tests with the factory and follow production against the approved sample. Send us your models.
Paint, finish and colour
Decide early whether you sell the part primed, painted in body colours or in a fixed finish, because that choice changes the factory, the packaging and the returns.
There are three common ways to sell louvres and spoilers:
- Primed only: the buyer has it painted locally to match the car. Fewer stock items, but the buyer pays a body shop.
- Painted to body colour: ready to fit, but every colour is a separate stock item, and colour matching across batches has to be controlled.
- Fixed finish: matt black, gloss black or carbon look. One stock item per model, which is why many sellers start here.
For painted parts, a colour code alone is not enough. Ask for a painted sample panel per colour, keep it, and inspect production against it, and ask how each piece is wrapped so it does not rub in transit.
Rear visibility and the rules where you sell
A louvre reduces the view through the rear glass and a spoiler changes the vehicle’s outline, so confirm the current rule in the market where you sell before you list either product.
Rules on rear visibility, external projections and changes to a registered vehicle are set country by country, can differ between vehicle categories, and change.
Japan is one example we checked against the published text. A notice issued by the former Ministry of Transport and published today by the Ministry of Land, Infrastructure, Transport and Tourism (Jigi No. 234 and Jisei No. 262 of 16 November 1995, last amended on 11 June 2015) works with a companion notice (Jigi No. 235, last amended on 8 April 2003) that lists “designated parts”, including air spoilers and louvres. The main notice sets out three cases in which fitting a part does not count as a change to the length, width and height recorded on the vehicle inspection certificate:
| Case | Effect on the recorded length, width and height |
|---|---|
| Any part fitted by a “simple” method, one that can be removed easily by hand | No change to the record |
| A designated part fitted by a “fixed” method, one that is neither removable by hand nor welded or riveted | No change to the record |
| A designated part welded or riveted on, or any other part fitted by a fixed, welded or riveted method | No change to the record if the vehicle stays within ±3 cm in length, ±2 cm in width and ±4 cm in height of the recorded figures |
The notice applies the same three cases to the recorded vehicle weight, with a range of ±50 kg for small vehicles and light vehicles subject to inspection, and ±100 kg for ordinary and large special vehicles.
That is not the same as “anything goes”. The vehicle must still meet the safety standards with the part fitted, and a note to the list says body-exterior parts a pedestrian or cyclist could touch must not have sharp or pointed edges facing outward.
For any other market, ask your importer, your customs broker or a vehicle inspection body for the current rule, and keep the answer on file with the product’s specification.
Design rights, logos and liability
Make your own design, keep vehicle makers’ logos off the part, and settle liability and quality terms before the first order.
Some factories offer “original-style” spoilers that copy a vehicle maker’s factory part. Design rights and trademarks apply in the country where you sell, wherever the part was made. A part that fits the same mounting points with your own shape is a safer product to build a brand on.
If a spoiler leaves a car on the motorway, the claim can reach the company that imported and sold it. How importer liability works in Japan and the EU is covered in our car accessory OEM guide; the practical step here is to write the mounting tests and the inspection standard into your purchase agreement.
What drives cost and MOQ
Louvre and spoiler costs are set mostly by whether a mould exists for the model, the material and process, and how many finishes you want.
We do not quote prices or minimum quantities before the part and the models are defined, because they change factory by factory. These are the drivers:
| Driver | Effect |
|---|---|
| Existing mould for the model | Stock items possible in smaller quantities; a new mould needs volume to pay it back |
| Material and process | Injection moulding needs a costly mould but low unit cost; composites need cheaper tooling but more hand work |
| Finishes and colours | Each painted colour is a separate run and a separate stock item |
| Mounting kit | Tape grade, brackets, bolts and templates all add to the bill of materials |
| Packaging | Long, fragile parts need custom cartons with their own minimums |
If you pay for a new mould, agree in writing who owns it, where it is kept and what happens if you move production. Our note on mould ownership agreements sets out the clauses; they apply wherever the mould is made. When comparing factories in different countries, line them up on landed cost rather than unit price.
For other exterior lines, see our guides to door visors, side steps and roof racks.
💬 Ready to source louvres or spoilers? See how our car accessories OEM service works, or send us your models and markets and we will come back with the factories that fit.
The groundwork is the same for every item: the fitment data the factory needs, what drives mould cost and packaging for online marketplaces.
Frequently asked questions
1. Should I choose tape or bolts for a rear spoiler?
It depends on the size and weight of the spoiler and on your buyers. Tape avoids drilling and suits lighter parts, provided the tape grade and surface preparation are right. Bolts give the strongest hold for larger spoilers but require drilling and sealing. Whichever you choose, agree adhesion or pull tests with the factory and trial a fitted sample on a vehicle.
2. Is a rear window louvre legal to fit?
It depends on the country and the vehicle category. In Japan, louvres are on the list of designated parts in the transport ministry’s notice, but the vehicle must still meet the safety standards with the part fitted. For other markets, confirm the current rule with your importer or a vehicle inspection body before you list the product.
3. Can a factory paint the spoiler to match the car’s colour?
Many can, but each colour becomes a separate production run and a separate stock item. Ask for a painted sample panel per colour, keep it as the reference, and inspect production against it. Many sellers start with a fixed black or primed finish to keep the range manageable.
4. Can I sell a spoiler that copies the vehicle maker’s original design?
That is risky. Design rights and trademarks apply in the country where you sell, wherever the part was made. A part that uses the same mounting points but has your own shape, with no vehicle maker’s logo, is a safer basis for your brand.
5. What information should I send a factory first?
The model code, years and body type, the market specification, whether you want a louvre or a spoiler, the material and finish, your preferred mounting method, and the rough quantity per model. Add photos of the tailgate showing the wiper, stop lamp and any camera, so the factory can check clearances.
Sources
Checked on 24 October 2026.
- ISO 4892-2:2013, Plastics — Methods of exposure to laboratory light sources — Part 2: Xenon-arc lamps (ISO): https://www.iso.org/standard/55481.html
- Former Ministry of Transport, Notice Jigi No. 234 and Jisei No. 262 (16 November 1995, last amended by Kokujigi No. 67 and Kokujisei No. 55 of 11 June 2015), as published by the Ministry of Land, Infrastructure, Transport and Tourism, on the treatment of vehicles fitted with automotive parts (in Japanese): https://www.mlit.go.jp/notice/noticedata/pdf/20210804/jidousha1-1.pdf
- Former Ministry of Transport, Notice Jigi No. 235 (16 November 1995, last amended by Kokujigi No. 6 of 8 April 2003), list of designated parts, as published by the Ministry of Land, Infrastructure, Transport and Tourism (in Japanese): https://www.mlit.go.jp/notice/noticedata/pdf/20210804/jidousha1-2.pdf