Oil resistance? Grease resistance? What's the difference?
Broadly speaking, we consider liquids such as machine oil and olive oil to be to be just that—oil. Greases, on the other hand, tend to be thicker and not likely to flow. Wheel bearing grease, shortening and room-temperature meat fats are some examples of greases. That last example—room-temperature meat fat—brings up an important point to keep in mind. Temperature can convert a grease to our definition of an oil, and vice-versa. Heat up meat fat and it quickly changes into a very penetrating oil.

There’s also a major distinction to be made between petroleum-based oil/grease and animal oil/grease. While the former is largely pure hydrocarbon, the latter usually contains some significant percentage of water. This distinction can be an important factor in selecting a barrier coating, especially in those cases where product freezing is concerned.

Why are oil and grease resistance important?
Petroleum-based oils are highly-penetrating and even a small amount can severely darken kraft paper fibers. And you know how unsightly an oil-stained package can be! Kraft paper, being highly absorbent, can literally suck the protective oils right off of metal parts, robbing them of their intended protection.

Food oils and greases cause similar problems, but generally to a lesser degree. And here’s where that water component comes into play. A great grease barrier without any water resistance will allow the moisture of the product to penetrate the paper, weakening it. Frozen meats can then actually bond themselves to the box through a process we call “frost bonding”.

How are oil and grease resistance measured?
Both are tested with a 3M Test Kit , which subjects the coated sample to a series of increasingly-potent blends of oil and solvent, numbered from 1 (low) to 12 (high). The number of the most potent blend which does not penetrate the coating is called the “kit rating”. Level 1 involves just an oil, and a fairly benign one at that, so it’s not too hard to achieve a kit rating of “1”. At the other end of the test spectrum is Level 12, which uses no oil and an extremely potent solvent. Achieving a Kit Rating of “12” is very difficult, but possible.

Michelman grease & oil resistant coatings
Listed below are those Michelman coatings which are commonly used or recommended for grease & oil resistant applications. Many of these coatings have multiple properties and will appear on other cross references as well.