Core What is fed and how hard it is drafted

Core Supply Linear Density tex

7.8 tex is 78 dtex, a common elastane

Core Draft x

Core Fibre Density g/cm3

Elastane about 1.21, polyester 1.38

Yarn The finished strand

Finished Yarn Linear Density tex

Yarn Bulk Density g/cm3

Packing density of the spun strand, not the fibre

Core Ratio by Mass

— %

Delivered core against the finished yarn

Core, Sheath & Cover

Core Inside the Yarn: — tex
Sheath Linear Density: — tex
Sheath Wall Thickness: — um
Core Diameter: — um
Yarn Diameter: — um
Cover as a Share of Yarn Radius: — %
Core Stretch Held in the Yarn: — %
Sheath to Core Mass Ratio: — x

Both strands are treated as solid circular sections, which is reasonable for the elastane monofilament and only nominal for the spun yarn - a real spun yarn is neither circular nor uniform along its length. The cover thickness is therefore a design figure for comparing constructions, not a measurable wall. Core concentricity is not modelled at all and is the dominant real-world variable: an eccentric core can reduce the local wall to near zero while every figure here is unchanged. The stretch potential shown is the core draft expressed as a percentage and represents the extension stored in the core, not the stretch the finished fabric will exhibit, which depends on the construction and on the finishing. Elastane linear density is nominal and drifts with package build as the feed tension changes.

Core-Spun Yarn Core Ratio, Sheath Cover & Stretch Potential — free, with the formula and a worked example, at Textile School.