Which of these aspects is used to determine bed sheet quality?

Thread count measures the number of yarns used per square inch of fabric and is mainly relevant for cotton sheets. However, measuring thread count isn’t your only tool when looking for high-quality sheets. To determine the overall quality of bed sheets, consider factors beyond thread count. These include the type of fibers used (e.g., cotton, Tencel, bamboo), the staple length of the fibers (longer staples are softer), and the weave pattern (e.g., percale for breathability, sateen for a smooth feel). High-quality sheets often feature long-staple fibers and durable weaves.

Source: Amerisleep