What does 'grain line' refer to in fabric?

The term 'grain line' specifically refers to the direction of the fabric fibers in a piece of material. Understanding the grain line is crucial in textiles and sewing because it affects how the fabric drapes, stretches, and behaves when sewn.

Fabrics usually have three types of grain lines: lengthwise grain, crosswise grain, and bias grain. The lengthwise grain runs parallel to the selvage edge of the fabric, while the crosswise grain runs perpendicular to the selvage. The bias grain is at a 45-degree angle to both the lengthwise and crosswise grains. When cutting patterns or pieces from fabric, aligning them with the grain line ensures that the final product drapes and fits properly, maintaining the intended design and structure.

Options referring to the length, thickness, or printed patterns do not capture the definition of 'grain line,' highlighting the importance of knowing the direction of the fibers in effective fabric usage.