From measurement to control - Unlocking the value of Online air Permeability in papermaking
In modern papermaking, mills continuously strive to improve process stability, product quality, and cost efficiency. While parameters such as basis weight, moisture, and thickness are routinely measured online, sheet structure often remains a blind spot.
One of the most powerful indicators of sheet structure is porosity. In practical mill operations, this is expressed and controlled through air permeability.
Porosity refers to the internal structure of the paper — the network of pores and voids within the sheet. Air permeability, on the other hand, describes how easily air flows through that structure.
Porosity is the structure. Air permeability is the measurable signal.
Traditionally, air permeability has been measured in the laboratory. While accurate, this approach introduces a delay between production and feedback. By the time results are available, large volumes of paper may already be produced.
This delay leads to reactive process control and often results in:
Over-refining
Excess chemical dosing
Longer grade change times
Online air permeability measurement transforms this situation. Instead of a delayed quality indicator, it becomes a real-time process control variable. Operators can immediately see how process changes affect sheet structure and respond accordingly.
With ACA Permi Online, operators can immediately see how process changes affect sheet structure and respond accordingly.
Key process benefits include:
Refining optimization:
Refining is one of the most energy-intensive operations. Real-time air permeability allows reduction of safety margins and avoidance of over-refining.Improved dewatering and drying:
Stable sheet structure improves press performance and reduces drying energy demand.Reduced chemical consumption:
More stable structure reduces the need for “insurance dosing” of additives.Faster grade changes:
With immediate feedback, mills can reach target specifications faster, reducing off-spec production.
Air permeability is a product itself
For many specialty grades, air permeability is not just a process parameter — it defines product performance:
- Filter papers: flow resistance and filtration efficiency
- Sack papers: air release during filling
- Cigarette papers: burn rate (CORESTA)
- Battery separators: electrolyte transport
In these cases, controlling air permeability means controlling the product.
The economic impact is significant. Even small improvements translate into large annual savings. For a mill producing 150,000 tons per year, a saving of just 1 €/ton equals 150,000 € annually.
Typical combined benefits:
- Energy savings: 3–8% in refining, 2–5% in drying
- Chemical savings: ~0.5–1.5 €/ton
- Grade change improvements: 20–50% faster transitions
This results in total savings of approximately 2–5 €/ton, corresponding to 300,000–750,000 € per year.
With an investment level around 60,000 €, payback is typically achieved within months.
In conclusion, online air permeability measurement bridges the gap between process and product. It enables mills to move from reactive quality control to proactive process control.
In porosity-driven grades, this goes even further: controlling air permeability means controlling the final product performance.
Online measurement turns sheet structure into a controllable variable — unlocking both process stability and economic value.
About ACA Permi Online
ACA Permi Online is a well-established and trusted solution for online air permeability measurement in the papermaking industry.
With 40 years of experience, ACA Systems has supported paper mills worldwide in transforming porosity from a laboratory parameter into a reliable real-time process control variable.
Across its lifetime, ACA Permi has been successfully implemented in numerous installations, covering a wide range of paper grades — from packaging and specialty papers to highly demanding porosity-driven applications such as filtration and cigarette papers.
The system is designed for:
continuous, real-time air permeability measurement
robust operation in demanding mill environments
direct integration into process control strategies
ACA Permi Online enables mills to improve:
process stability
product consistency
energy and chemical efficiency
Learn More
Curious how real-time air permeability could impact your process efficiency and product quality?
Contact us to see how ACA Permi Online can support your mill — from improved stability to measurable cost savings.
Backed by over 40 years of experience and a strong global track record, ACA Permi helps mills control what truly matters: sheet structure.
