Reading the Spec Sheet

This appendix defines the vocabulary manufacturers use on datasheets. Chapter 1 introduces denier, grams per square metre (g/m²), and ounces per square yard (oz/yd²) and the conversion between them; that math is not repeated here.

Warp and fill

Woven cloth has two perpendicular yarn directions. Warp runs lengthwise with the roll (machine direction). Fill (weft) runs crosswise. Tear strength, tensile strength, and stiffness are usually reported separately in warp and fill because weave geometry and yarn counts differ by direction. Laminated fabrics add scrims and films, so warp/fill numbers still appear: they describe the finished composite on the test fixture, not the face yarn alone unless the datasheet says so.

Tear strength

Tear strength is the force required to continue a tear that already started, not the force to initiate one. Common textile standards include ASTM D2261 (tongue tear) and ASTM D1424 (Elmendorf). Results are quoted in newtons (N) or pounds-force (lbf). X-Pac listings often pair warp and fill because the bias X-PLY affects each direction differently.

Abrasion: Taber (ASTM D3884)

ASTM D3884 (Taber abrasion): a specimen rotates under weighted abrasive wheels; each revolution is one cycle. The run continues until the fabric meets a failure criterion (typically a hole or structural breakdown), or until a manufacturer-defined endpoint. Higher cycle counts mean more rotations before failure under that lab’s declared procedure.

Comparing Taber numbers across brands is fuzzy: wheel compound, load, and endpoint definitions vary. Comparing numbers within one manufacturer’s sheet family (VX21 vs VX42 on X-Pac.com, or EPX200 vs EPX400 on Challenge’s listings) is usually meaningful because the same lab applies one protocol.

Face-only vs laminate: Some informal figures quote abrasion on the face textile before lamination. Consumer-facing X-Pac pages quote Taber on the full laminate unless labeled otherwise, which is why a single material can appear under two different cycle counts in the wild.

Hydrostatic head and “200+ psi”

ISO 811 and AATCC 127 measure resistance to liquid water under pressure: hydrostatic head. Water presses on one side of a clamped specimen until penetration is observed. Results may be reported as a water column (millimetres of water, mm H₂O), as bar, or as psi. X-Pac’s “13.8+ bar / 200+ psi” line is the same class of test expressed in pressure units, describing the film-containing composite resisting forced water entry, not everyday rain simulation and not sweat-vapour breathability.

Cross-brand and retrieval-date caveat

Treat maker-published figures as comparable within that maker’s own tables, not as objective rankings across Cordura, X-Pac, EcoPak, and Ultra unless the same independent lab published all of them under one protocol. Mills revise coatings and adhesives without fanfare, so note the retrieval month when citing numbers from public websites (this book uses May 2026 for Dimension-Polyant X-Pac product pages where cited in Chapter 3).