Fabric Drape Coefficient Calculator

The Cusick drape test is a standard textile-science method for measuring how a fabric hangs and folds under its own weight. A circular fabric sample rests on a smaller support disc; when the fabric is illuminated from above, it casts a shadow shaped by however many folds it forms as it drapes over the disc's edge. The drape coefficient compares that shadow's area to two reference areas -- the support disc's flat area and the sample's own flat, undraped area -- and expresses the difference as a percentage: (draped shadow area minus support area) divided by (flat sample area minus support area), times 100. A coefficient near 0% means the fabric collapses almost flat against the support, forming a shadow barely bigger than the disc -- the hallmark of a fluid, limp fabric like a lightweight rayon or silk.

A coefficient near 100% means the fabric barely folds at all, so its shadow is nearly as large as the flat, undraped sample -- typical of stiff fabrics like heavy canvas or interfaced material. Because draping only folds fabric inward, the draped shadow can never be smaller than the support disc or larger than the flat sample, so a real drape coefficient always falls between 0% and 100%; this calculator holds the result in that range even if the entered diameters describe a physically inconsistent test setup. Drape Classification sorts that percentage into five labeled bands (Very Limp through Very Stiff) as an illustrative, easy-to-read simplification -- published drape-test literature we could verify cites only two named reference points (very limp fabrics around 30%, very stiff ones around 85%), not five bands with these specific cut points, so treat the labels as a rough guide rather than an official classification standard. The Estimated Nodes figure is a rough count of how many distinct folds a drape of that coefficient typically forms, and Bending Rigidity is a simplified structural estimate driven by fabric weight and thickness rather than the drape measurement itself -- it does not come from the Cusick test.