  Knitting turns yarn, a 1D material, into a 2D fabric that is flexible,
durable [1], and can be patterned to adopt a wide range of 3D geometries [2].
Like other mechanical metamaterials [3], the elasticity of knitted fabrics is
an emergent property of the local stitch topology and pattern that cannot
solely be attributed to the yarn itself. Thus, knitting can be viewed as an
additive manufacturing technique that allows for stitch-by-stitch programming
of elastic properties and has applications in many fields ranging from soft
robotics [4-6] and wearable electronics [7,8] to engineered tissue[9] and
architected materials [10,11]. However, predicting these mechanical properties
based on the stitch type remains elusive. Here we untangle the relationship
between changes in stitch topology and emergent elasticity in several types of
knitted fabrics. We combine experiment and simulation to construct a
constitutive model for the nonlinear bulk response of these fabrics. This model
serves as a basis for composite fabrics with bespoke mechanical properties,
which crucially do not depend on the constituent yarn.
