The process of adding fabric layers held together with stitches is known as?

The process of adding fabric layers held together with stitches is known as quilting. This technique typically involves stitching multiple layers of fabric together, usually with a layer of batting in between, to create a thicker, padded material. Quilting can be done by hand or with a sewing machine, and it not only serves functional purposes, such as providing warmth, but also allows for creative expression through patterns, designs, and textures. The art of quilting has a rich history across various cultures and has evolved into a recognized craft with numerous styles and techniques.

The other methods listed involve different processes: forging is associated with shaping metal, sand casting is a technique used in metalworking to create objects from molds, and felting involves matting fibers together, typically wool, using moisture and agitation. These practices do not involve layering fabric with stitches as quilting does, which highlights the unique characteristic of the correct answer.