Unlike other heavy cotton fabrics like denim, which use a twill weave, canvas is constructed using a plain weave or a duck weave. In a plain weave, the warp (vertical) and weft (horizontal) threads cross each other in a simple over-under pattern. In a duck weave, two or more threads are grouped together in parallel, creating an even tighter, more compact texture. This dense weave makes the material highly resistant to tearing, puncturing, and harsh weather conditions.