What method involves applying pressure and heat to transform fibers into fabric?

The method that involves applying pressure and heat to transform fibers into fabric is felting. Felting is a fabric production process where wool or other animal hairs are agitated, often through friction, heat, and moisture. This process causes the fibers to interlock and bond together, creating a dense and non-woven fabric. Unlike other methods of fabric creation, felting does not involve weaving or knitting processes that interlace or interloop yarns; instead, it directly transforms loose fibers into a cohesive material.

In contrast, weaving involves interlacing vertical and horizontal threads, knitting constructs fabric through interlooping yarns, and spinning primarily refers to the process of twisting fibers together to form yarns, which are then used in weaving or knitting. Felting stands out because it utilizes heat and pressure directly on the fibers to create a solid fabric structure without the use of a loom or knitting needles. This unique characteristic of felting is what makes it the correct answer.