3 Numbers That Define High-Performance Greaseproof Paper
Created on 08.26
While many factors contribute to the quality of greaseproof paper, three numbers are particularly critical for defining its high-performance characteristics. These numbers are measurable, scientific, and tell you exactly what to expect from the product.
The 3 numbers that define high-performance greaseproof paper are:
1. Kit Rating ≥ 12
2. Gurley Hill Porosity > 1000 seconds
3. Basis Weight (GSM) 35 - 50
Here’s a detailed breakdown of what each number means and why it's so important.
1. Kit Rating (Grease Resistance)
- The Number: ≥ 12 (Often 12, but high-performance papers can be 15+)
- What It Measures: This is the definitive test for a paper's resistance to grease and oil. It measures how long it takes for grease to penetrate and show a visible stain on the other side under standardized conditions.
- How It Works: The test uses a series of castor oil and toluene solutions numbered 1 through 12 (each "Kit" is a specific blend). A Kit 12 solution is 100% pure castor oil—the most challenging substance to block. A Kit Rating of 12 means the paper withstood 100% castor oil for the entire duration of the test (typically 15 minutes) with no penetration or stain. A lower rating (e.g., Kit 5) means it could only resist a much weaker, more diluted solution.
- Why It Defines Performance: This is the paper's primary job. A high Kit Rating (12 or above) guarantees it will effectively block fats, oils, and greases from even the greasiest foods like fried chicken, bacon, pizza, and pastries, preventing leaks, soggy packaging, and stained surfaces.
2. Gurley Hill Porosity (Air Resistance)
- The Number: > 1000 seconds (The higher, the better. Some specialty papers exceed 10,000 seconds).
- What It Measures: This test measures the density and tightness of the paper's fiber structure. It records the time in seconds it takes for 100 mL of air to pass through a single square inch of the paper under a specific pressure.
- How It Works: A sample is placed in a Gurley Densometer. A cylinder of air is released, and a timer measures how long it takes to pass through the paper. A very low number (e.g., 10 seconds) indicates a porous, breathable paper like a coffee filter. A very high number (e.g., 1200 seconds) indicates an extremely dense, non-porous sheet—the hallmark of true greaseproof paper.
- Why It Defines Performance: Porosity is directly linked to grease resistance. Grease and oil can't penetrate a structure that air can't easily pass through. A high Gurley number means the fibers are highly refined and packed tightly together, creating a physical barrier with no easy pathways for grease to migrate through. It also contributes to the paper's strength when wet.
3. Basis Weight (Grammage)
- The Number: 35 - 50 grams per square meter (GSM)
- What It Measures: This is the weight (in grams) of one square meter of the paper. It’s a direct indicator of the paper's thickness, substance, and durability.
- How It Works: It's a simple measurement of weight over area. While not a direct measure of thickness (that would be caliper or microns), a higher GSM generally correlates with a heavier, more robust paper.
- Why It Defines Performance:
- Too Low (<35 GSM): The paper feels flimsy, is more likely to tear during handling, and may not have enough fiber mass to provide a reliable grease barrier, even with a good Kit rating.
- Ideal Range (35-50 GSM): This is the sweet spot for high-performance food service paper. It provides excellent strength and tear resistance without being overly thick or rigid. It feels substantial in the hand and can withstand the weight of hot, greasy food without failing.
- Too High (>60 GSM): The paper becomes more like a board, losing the flexibility needed for wrapping and increasing material costs unnecessarily.
Putting It All Together: What to Look For
When evaluating a high-performance greaseproof paper for professional use (e.g., a bakery, food truck, or restaurant), you should look for a product that specifies:
"This paper has a Kit Rating of 12, a Gurley Hill porosity of over 1000 seconds, and a basis weight of 40 GSM."
These three numbers together provide a complete, technical picture of the paper's performance, far more reliably than marketing terms like "extra strong" or "super greaseproof." They tell you it will be highly resistant to grease, made from a dense fiber structure, and have the physical strength to perform its job reliably.
Ray
Ferrill
Evelyn