Cast or Calendered Vinyl: What Channels and Curves on a Vehicle Demand

The panel van has just been lettered, and the lettering runs neatly across two body channels. Some time later, the vinyl in the channels is no longer touching the metal. It spans across them like a cloth over a gutter, and along the edge you can see a fine line where it used to be stuck.

That may be down to the installation. But the mistake may have been made earlier, at the question: cast or calendered vinyl? On flat metal you hardly notice the difference. As soon as channels or curves come into play, you certainly do.

The information is based on the film manufacturers' application guidelines; if in doubt, the data sheet for the specific film applies. This article does not cover legal questions.

Cast or calendered vinyl: the difference lies in how it is made

Calendered vinyl is drawn flat from a PVC compound between rollers and stretched in the process. That tension stays in the film. The process is the more economical one and is used mainly for films intended for short- to medium-term outdoor exposure. Calendered vinyl comes in monomeric and polymeric versions. How they differ is a topic of its own.

Cast vinyl is made differently. Liquid PVC paste is cast onto a carrier paper, dried in an oven and then released from the carrier. As a result it has little internal tension and hardly shrinks.

Calendered vinyl behaves like a stretched rubber band taped to a table. Cast vinyl is more like modelling clay: it stays in the shape you press it into.

Casting does allow very thin films, but cast doesn't automatically mean thinner. The thickness in micrometres (µm) won't tell you which kind of film you have in front of you.

What happens on the vehicle: channels, rivets, curves

On a flat door, the tension in calendered vinyl is hardly an issue. It gets tricky as soon as the film has to take on a shape. Stretched film wants to go back to its old shape. Calendered vinyl shrinks more over time than cast vinyl and can pull back at edges and channels. Then the old adhesive line becomes visible, or the film lifts.

Body channels and corrugated panels

In a channel, the tension acts like a spring. The film wants to return to a flat surface and comes away from the recess. According to the film manufacturers' application guidelines, calendered vinyl must therefore not be heat-stretched into deep body channels. It is not pulled into them; instead it is cut and applied with an overlap.

Cast vinyl isn't simply pulled into sharp-edged or deep channels either. Professional installers work there with inserted pieces of film (inlays) or relief cuts and apply them with an overlap. That is what the application guidelines specify. How far a film may be stretched in a channel and how it is handled there is set out in the guideline for the specific film.

Rivets

Over a rivet head, the film likes to stand up like a small tent. Professional installers puncture the air bubble, warm the film and press it down around the rivet. For surfaces with rivets, manufacturers recommend cast vinyl. Calendered vinyl is cut over rivets and applied with an overlap.

Compound curves: bumpers and wheel arches

A simple curve, such as a slightly rounded door, can usually be handled by calendered vinyl too, provided the data sheet allows vehicle use. If the surface curves in two directions, the film has to be stretched, and that is exactly the stretch it wants to get rid of again. For pronounced 3D shapes, manufacturers recommend cast vinyl. The data sheet of one cast film also requires a higher minimum application temperature for complex curves than for flat surfaces.

Then there is post-heating. When the stretched areas are heated in a targeted way, the tension is released, and only then does the film keep its new shape in a channel or curve. There is no temperature that suits every film. It is given in the data sheet and, according to the application guidelines, measured with an infrared thermometer. Professional installers keep the heat gun moving and stay below the upper temperature limit in the data sheet, because too much heat can damage the film, and some plastic parts can barely tolerate heat at all. On a vehicle, this is a job for a professional, not for a Saturday afternoon in the garage.

Where calendered vinyl is good enough on a vehicle

Calendered vinyl has its place on vehicles. Manufacturers recommend it for vehicles and vehicle parts without pronounced 3D shapes. In practice that means, for example, a logo on a smooth door or partial lettering on the flat side panel between the channels, especially for short- to medium-term projects.

One manufacturer of calendered vinyl writes that modern calendered films have less tension and shrink less than older ones. That may be true of newer films, but it doesn't make them the film for channels and rivets. There, the rule from the application guidelines still applies: cut rather than pull in.

Also check the application information in the data sheet. Some low-cost calendered films are ruled out entirely for vehicle lettering by the manufacturer. Our standard sticker suits flat, smooth areas of a vehicle; for channels, rivets or a full wrap we advise you on the right vehicle film. For vehicles, we advise you on the right film.

How to tell before ordering which film your vehicle needs

Walk once around the vehicle with the design in your hand. Where should the lettering go, and what does the metal look like exactly there?

• Flat or gently curved: Calendered vinyl is an option here, provided the data sheet allows vehicle use.
• Channels, corrugated panels, rivets: Here manufacturers recommend cast vinyl. Installation belongs in experienced hands.
• Compound curves: Bumpers and wheel arches need a film that is approved for such shapes.

Not all cast vinyl is the same. Every data sheet lists the surfaces the film is approved for: flat, with rivets, simple or compound curves, corrugated panels or channels, deep recesses. According to the manufacturers' data sheets, thicker overlaminates and films with a textured surface conform less well. Carbon and other textured finishes are therefore trickier in a channel than smooth film.

Compare shrinkage values: Data sheets state how much the applied film shrinks. However, manufacturers measure differently, sometimes in percent, sometimes in millimetres. So only compare values that were measured the same way.

Think about the laminate: The protective laminate also comes in cast or calendered form. Which laminate goes with which print film is set by the manufacturers. For some films they expressly prescribe it. With printed vehicle vinyl, ask about both: film and laminate.

Keeping track later: One manufacturer, for example, prints only a batch number on the back; the type of film is not stated there. Have the film named in the quote and keep the data sheet, and you will still know later what was applied.

Typical failure patterns

• Vinyl lifting out of the channel: According to one film manufacturer's application guideline, lifting from sharp-edged channels is a known problem, especially on delivery vans and panel vans. It can happen even with the right film.
• Visible adhesive line: Usually the film has shrunk, often in the case of calendered vinyl, and shows at the edge where it once was.
• Frayed, finger-like edges: a typical sign of overstretched film.
• Lines along the edge: If the film is pressed down near the edge while under tension, permanently visible adhesive lines can appear. According to the application guideline, the film is allowed to cool briefly after heating and then pressed down without tension. On stretched edges it can shrink and fade.

Over the years, within the durability stated in the data sheet, one manufacturer's application guideline counts a loss of gloss, slight colour changes, some lifting at edges and around rivets and, in the end, fine cracks as normal ageing. If the film lifts shortly after installation, that is a different matter. Edges, corners, weld seams and rivets count as critical points and are cleaned and dried particularly thoroughly before application.

The second attempt on the panel van

This is how it might have gone with the panel van from the beginning: a trade business has its lettering printed on a low-cost film and applies it itself, straight across the side channels. That is exactly where the film later gives way.

On the second attempt, the metal is looked at first: where are the channels and how deep are they, where are the rivets? Then the choice falls on a cast film that the data sheet approves for channels and rivets, with the laminate the manufacturer specifies for it. The installation is handled by a professional who splits the film at the deep channels as the guideline requires. Sharp-edged channels remain tricky, but film and surface now match.

Why the metal comes before the price per metre

The shape of the vehicle decides the film, not the price per metre. That is what our founder's more than 30 years in the trade come down to, and we have worked that way since the company was founded in 2017.

Cut corners at the channel and you risk applying it twice. And the second time, the old film has to come off first. Conversely, not every piece of door lettering needs cast vinyl. On a smooth surface, calendered vinyl is often the sensible choice.

The application guidelines do not provide for one continuous, uncut piece of film over every deep channel. You can read more about lettering company vehicles under Professional vehicle wrapping.

Conclusion: what the metal tells you about the film

On a vehicle, the question “cast or calendered” is answered by the surface. Smooth and gently curved surfaces can usually be handled by calendered vinyl too, if the data sheet allows vehicle use. For channels, rivets and compound curves, manufacturers recommend cast vinyl, and installation there belongs in experienced hands. Before ordering, clarify:

• The surface: Will the lettering sit on flat metal, across channels, over rivets or on a compound curve?
• The data sheet: Is the film approved for vehicles and for exactly these shapes, and which laminate goes with it?
• The installation: Will you apply it yourself on flat surfaces, or will a professional handle the difficult spots?

Our sign-making team will advise you on the film for your vehicle and handle the installation if you wish. You'll find the service under Vehicle graphics. Or write to us via Contact and tell us which vehicle it is and where the lettering should go.

Frequently asked questions

What is the difference between cast and calendered vinyl?

Calendered vinyl is rolled to thickness between rollers and stretched in the process. The tension stays in the film, which is why it shrinks more. Cast vinyl is made from liquid PVC paste that dries on a carrier. It has little internal tension and hardly shrinks. You can't tell the difference from the thickness alone.

Is calendered vinyl good enough for vehicle lettering?

On flat and gently curved surfaces it often is, for example for a logo on the door, provided the data sheet allows vehicle use. Some low-cost calendered films are ruled out for vehicles by the manufacturer. For channels, rivets and compound curves, manufacturers recommend cast vinyl.

Why does vinyl lift out of a body channel?

Stretched vinyl wants to return to its original shape. Calendered vinyl shrinks more and can pull back out of channels. That said, even the right film can come away from sharp-edged channels. According to the film manufacturers' application guidelines, vinyl in deep or sharp-edged channels is cut and applied with an overlap, and stretched areas are post-heated as specified in the data sheet.