Why replace the risk score?

Because it could not be checked or acted on. It averaged three numbers the user invented and published the result to one decimal; nothing anchored the inputs, two engineers would disagree, and the output corresponded to no physical quantity. Inhibition has a physical expression. A depth of uncured film, which is measurable, comparable and directly connected to whether the product is acceptable.

Why does a thin film suffer more?

Because the inhibited layer is set by surface chemistry and oxygen diffusion, not by how much material is underneath it. Roughly the same depth is affected either way, so it is 5% of a 200 µm casting and 40% of a 25 µm coating. Below about the layer depth, the whole film is inside the inhibited region and effectively nothing cures.

Will slowing the line help?

No, and this is the most useful thing on the page. Inhibition is a competition between radical generation and oxygen diffusing back into the surface, so it is won by INTENSITY rather than by time. A longer exposure at the same irradiance replenishes oxygen as fast as it is consumed and extends the stalemate. More peak irradiance, an inert atmosphere, a barrier film, or a surface-active photoinitiator all attack the actual mechanism.

Why won't the page predict the inhibited layer depth?

Because it depends on photoinitiator type and concentration, resin viscosity and oxygen solubility, irradiance and temperature, interacting in a way no closed form captures honestly. A page that produced a number from irradiance and oxygen alone would be inventing a model and dressing it as physics. Measuring it takes one cured sample, and that measurement is specific to your process in a way no published figure can be.

How much does nitrogen actually help?

Enough to be the standard answer in inks and varnishes, and not in a proportion this page can state. Dropping from air to a few hundred ppm is a several-hundred-fold reduction in oxygen and typically shrinks the inhibited layer dramatically, but the relationship is non-linear and formulation-specific. Trial it at the level you can actually hold, measure the layer again, and price it on the nitrogen page.

Can I just accept the inhibited layer?

Sometimes, and it is worth asking rather than assuming. A thin tacky layer under a subsequent coat may be harmless or even helpful for intercoat adhesion; one on a finished surface is a defect. What it must not be is ignored where it becomes a weak boundary layer under an adhesive bond, because there it produces a joint that tests well initially and fails in service.

UV Curing calculator

UV Oxygen Inhibition Calculator: How Much of the Film Stays Uncured

Express oxygen inhibition as the physical thing it is: a depth of film at the surface that never fully cures. Enter the film thickness, the inhibited layer depth measured in a trial, the cure-zone oxygen today and the level a purge would hold. The calculator returns the fraction of the film left uncured, the depth that does cure, and what the proposed inerting buys in oxygen terms. It replaces the earlier page, which averaged three scores out of 100 into a number that corresponded to nothing.

What this calculator does

Express oxygen inhibition as what it physically is. A depth of uncured film, and show what fraction of a given coating that represents, plus what an inerting change buys in oxygen terms.
Use it for deciding whether surface tack is an inhibition problem or a dose problem, explaining why a thin varnish fails where a thick coating does not, quantifying what fraction of a film a measured inhibited layer represents, comparing an inerting proposal against a higher-irradiance one, recording the effect of an inerting trial in a usable form.
Express oxygen inhibition as what it physically is. A depth of uncured film, and show what fraction of a given coating that represents, plus what an inerting change buys in oxygen terms.

Formula used

Inhibited layer within this film = MIN(measured layer depth, film thickness)
Film thickness left uncured (%) = inhibited layer ÷ film thickness × 100
Film that cures = film thickness − inhibited layer
Cure-zone oxygen against air (%) = cure-zone ppm ÷ 209,000 × 100
Oxygen reduction factor = cure-zone ppm ÷ target ppm

Inputs explained

Film thickness: Wet film thickness of the coating, ink or adhesive layer. The input that decides whether an inhibited layer is a nuisance or the whole problem.
Inhibited layer depth (measured): Depth of uncured material at the surface, from a trial at your irradiance and atmosphere. No formula predicts this from first principles. It has to be measured.
Cure-zone oxygen now: Oxygen concentration in the cure zone today. Air is about 209,000 ppm.
Oxygen level being considered: The level a proposed nitrogen purge would hold. Reported as a reduction factor. How much less oxygen, not how much less inhibition, which only a trial can say.

How to use the result

Best suited to deciding whether surface tack is an inhibition problem or a dose problem, explaining why a thin varnish fails where a thick coating does not, quantifying what fraction of a film a measured inhibited layer represents, comparing an inerting proposal against a higher-irradiance one, recording the effect of an inerting trial in a usable form.
Does not predict the inhibited layer depth. That requires a trial, and any page claiming to compute it from irradiance and oxygen alone is asserting more than the physics supports. Does not convert an oxygen reduction into a layer reduction. The relationship depends on the whole formulation and is strongly non-linear. Assumes a uniform layer. In practice a still recess inhibits more than a face swept by moving air, and neither is the average. Ignores the surface's condition after cure. A partially inhibited layer may be tacky, may be rubbed off, or may remain as a weak boundary layer, and those are very different outcomes. Says nothing about the through-cure of the rest of the film, which is a dose question handled elsewhere.

Common questions

Why replace the risk score? Because it could not be checked or acted on. It averaged three numbers the user invented and published the result to one decimal; nothing anchored the inputs, two engineers would disagree, and the output corresponded to no physical quantity. Inhibition has a physical expression. A depth of uncured film, which is measurable, comparable and directly connected to whether the product is acceptable.
Why does a thin film suffer more? Because the inhibited layer is set by surface chemistry and oxygen diffusion, not by how much material is underneath it. Roughly the same depth is affected either way, so it is 5% of a 200 µm casting and 40% of a 25 µm coating. Below about the layer depth, the whole film is inside the inhibited region and effectively nothing cures.
Will slowing the line help? No, and this is the most useful thing on the page. Inhibition is a competition between radical generation and oxygen diffusing back into the surface, so it is won by INTENSITY rather than by time. A longer exposure at the same irradiance replenishes oxygen as fast as it is consumed and extends the stalemate. More peak irradiance, an inert atmosphere, a barrier film, or a surface-active photoinitiator all attack the actual mechanism.
Why won't the page predict the inhibited layer depth? Because it depends on photoinitiator type and concentration, resin viscosity and oxygen solubility, irradiance and temperature, interacting in a way no closed form captures honestly. A page that produced a number from irradiance and oxygen alone would be inventing a model and dressing it as physics. Measuring it takes one cured sample, and that measurement is specific to your process in a way no published figure can be.
How much does nitrogen actually help? Enough to be the standard answer in inks and varnishes, and not in a proportion this page can state. Dropping from air to a few hundred ppm is a several-hundred-fold reduction in oxygen and typically shrinks the inhibited layer dramatically, but the relationship is non-linear and formulation-specific. Trial it at the level you can actually hold, measure the layer again, and price it on the nitrogen page.

Last reviewed 2026-08-25.