What are the grades of U.S. folding boxboard?

U.S. folding boxboard grades aren't defined by single, universally agreed-upon "grades" like A, B, C, etc. Instead, they're categorized based on a combination of factors, primarily basis weight (weight per 1000 square feet) and strength properties. These properties are then used to determine the suitability for various applications. There's no simple A-B-C system like you might find in other paper products.

The key factors determining the type of folding boxboard are:

* Basis Weight: This is a crucial factor, indicating the thickness and overall strength of the board. Heavier basis weight generally means greater strength and durability.

* Surface Characteristics: This includes properties like smoothness, brightness, and printability. The surface will be tailored to the intended printing method and desired aesthetic.

* Stiffness: How well the board resists bending. Crucial for packaging applications requiring structural integrity.

* Bursting Strength: A measure of the board's resistance to internal pressure. Important for containers that might be filled with liquids or pressurized.

* Compressive Strength: Resistance to crushing forces, essential for stacking strength and protection of the contents.

* Fiber Composition: The type of fibers used (e.g., recycled content, virgin fibers) can impact properties and cost.

Manufacturers will often categorize their folding boxboards using internal designations based on the above characteristics to match the specific needs of the packaging application (e.g., "premium folding boxboard," "food-grade boxboard," "high-strength boxboard"). These designations are not standardized across the industry. To understand the grade, you'll need to refer to the specific manufacturer's specifications.