Quick Verdict
Striping mil thickness is how much paint or material is laid down, measured in mils (thousandths of an inch). It comes in two forms: wet film thickness, measured as the paint goes down, and dry film thickness, what remains after it cures. Thickness drives durability and reflectivity, because glass beads need enough material to hold them and enough film to survive traffic. Waterborne paint is commonly applied around 15 mils wet, while thermoplastic is far thicker, often 60 to 125 mils. Too thin and lines wear out in a season; too thick and beads sink and paint cracks.
What is a mil?
A mil is one thousandth of an inch (0.001 inch). It is the standard unit for paint film thickness because striping layers are far too thin to describe in fractions of an inch usefully. When we talk about a line applied at "15 mils," we mean the paint film is fifteen thousandths of an inch thick at application.
Do not confuse mils with millimeters. They are different units, and mixing them up leads to specs that are wildly off. In North American striping, mils is the working unit for film thickness, while line width is described in inches, as covered in our lane line striping standards.
Wet film vs dry film thickness
There are two thicknesses that matter, and they are not the same number.
- Wet film thickness (WFT) is measured immediately after application, while the paint is still wet. Crews check it with a wet-film gauge to confirm the sprayer is laying down the right amount.
- Dry film thickness (DFT) is what remains after the solvent or water evaporates and the film cures. Because waterborne paint loses volume as it dries, DFT is always less than WFT.
The gap between the two is the volume solids of the material. A paint with higher solids leaves more film behind per wet mil applied. That is why two coats specified at the same wet mils can leave different dry films if the products differ.
| Term | When measured | What it tells you |
|---|---|---|
| Wet film thickness | Right after spraying | Application rate is correct |
| Dry film thickness | After cure | Real durability of the line |
| Volume solids | Product property | How much wet becomes dry |
Typical thickness specs
Different materials live at very different thicknesses.
- Waterborne traffic paint: commonly around 15 mils wet for a standard line, sometimes more on rougher pavement.
- High-build waterborne: applied thicker where longer life is wanted.
- Thermoplastic: applied far thicker, often 60 to 125 mils, because it is a durable, plow-resistant material laid down hot.
- Glass beads: dropped or intermixed into the film; the film must be thick enough to embed the beads to roughly 60 percent for good retroreflectivity.
Thickness is not "more is always better." Beads sink and disappear if the film is too heavy, and thick paint on a cold or damp surface can skin over, trap moisture, and fail. The right build is matched to the material, the surface, and the weather.
Why thickness drives durability and reflectivity
Two things determine how long a stripe lasts and how well it shines at night: the material and how much of it is on the road.
- Durability: more dry film gives traffic more to wear through before the line disappears. On busy lanes, thin paint is a false economy because it triggers an early restripe.
- Retroreflectivity: glass beads are what make lines glow in headlights. Beads need to be seated in enough film to stay anchored and exposed at the right angle. Starve the film and beads pop out or bury, and night visibility drops.
In Oregon, where wet nights are the norm for much of the year, retroreflectivity is a safety issue, not a nicety. Proper film thickness and bead application keep centerlines and edge lines visible in rain and headlights.
Current Market Reality
Applying the correct film costs material, and material prices have climbed. Cutting mils to save paint is a common way to underbid a job and a common reason cheap striping fails fast. When you compare quotes, ask what wet mils and bead rate are specified, not just the price per foot.
Industry Baseline Range: long-line 4-inch paint striping runs about $0.15 -- $0.60+ per linear foot, and thermoplastic runs about $0.60 -- $2.50+ per linear foot, in part because of that much higher film build. Small jobs carry a $350 -- $1,000+ minimum callout. These are industry baseline ranges for planning only -- actual pricing depends on surface condition, layout complexity, material (paint vs thermoplastic), line footage, night/traffic-control needs, and current market conditions. Get a site-specific quote.
Oregon surface and weather effects
Pavement condition changes how much material a line needs. Rough, porous, or oxidized asphalt soaks up paint, so it may need a heavier application or a second coat to reach the target dry film. Fresh, tight asphalt holds film better. Temperature and moisture also matter: waterborne paint needs dry pavement and warm enough air to cure, which is why the May-to-October window works best across the Willamette Valley and I-5 corridor. Striping at the right thickness on damp or cold pavement still fails if the film cannot cure.
When film thins out from wear, the decision becomes whether to refresh or rebuild the layout, which we cover in maintenance versus full replacement.
How thickness is measured and controlled
Film thickness is not left to guesswork on a well-run job. Crews control it through equipment settings and verify it with simple tools, so the line that goes down matches the spec.
Wet film thickness is checked with a wet-film gauge, a small notched tool pressed into the fresh paint. The gauge reads which notches the paint touches, giving the wet mils on the spot. If the reading is low, the crew slows the truck or adjusts the spray so the next pass hits the target; if it is high, they speed up or reduce flow. On a long run, spot-checking wet film at intervals keeps the whole line consistent rather than heavy at the start and thin by the end.
Several variables drive the actual film laid down:
- Truck speed. Faster travel stretches the same paint volume over more distance, thinning the film.
- Spray tip and pressure. These set the flow rate and pattern width.
- Surface texture. Rough or porous asphalt absorbs paint, so it needs more material to reach the target dry film.
- Number of coats. A second coat builds film where one pass cannot reach the spec on a thirsty surface.
Dry film is harder to measure in the field because it requires the line to cure, but it is what the wet-film target is designed to produce. That is why specifying wet mils and bead rate up front, and checking them during application, is the practical way to guarantee the dry film you actually need. When a striping bid is unusually cheap, thin film is one of the first places corners get cut, and it does not show until the line wears out a year early. Asking for the film and bead spec, not just the price, protects the investment.
The Bottom Line
Striping mil thickness is one of the quiet specs that separates striping that lasts from striping that fades in a season. Wet film confirms the crew is applying enough; dry film is what actually survives traffic and holds your glass beads. Match the build to the material, the surface, and Oregon's weather, and your lines stay bright and visible far longer. Cojo is CCB Licensed and Insured, based in Hood River, serving statewide Oregon and the I-5 corridor. See our striping services or request a free estimate. For the full silo, start with our pillar on road striping and line painting in Oregon.