ASPECT RATIO: The luff length of the sail divided by the foot length.

BIAS: The direction diagonally across a piece of fabric at 45 degrees to the warp and fill.

COUNT: The number of fibers per inch in the warp or fill.

CREEP: Permanent, continuous elongation of a fiber under a sustained load

CRIMP: The "waviness" of the fiber or yarn when it is laid over and under fibers or yarns in a fabric. Crimp can contribute to the elongation of a fabric under load as it is "pulled out" of the loaded direction and "pushed into" the less heavily loaded direction.

CROSS-CUT: A sail panel layout in which the seams run roughly parallel to one another, typically perpendicular to the leech

DENIER: A measure of the weight of a continuous fiber filament. It is the weight in grams of 9,000 meters of a given fiber. The lower the number, the finer the fiber. Higher denier, heavier fibers are generally more rugged and durable.

DENIER PER INCH (DPI): A measure of the fabric's relative weight and strength, expressed as the number of fibers per inch, generally in the primary yarn direction.

ELONGATION: The difference between the initial length of a fabric sample and its length after stretching, expressed in 1/100ths of an inch.

FIBER: The basic entity that is twisted into yarns and then used in the production of a fabric.

FILAMENT: A single fibril of natural or synthetic textile fiber. Filaments are twisted or bunched to form fibers.

FILL (WEFT): The yarns or fibers that run across the width of the roll of fabric, perpendicular to the warp direction.

FILM: An extruded sheet of plastic, most often Mylar® polyester film. Film's desirable properties include low stretch, good bias stability, low porosity and good adhesion. Less desirable properties include low tear strength and relatively high physical shrinkage (due to creases and folds in the film).

FLEX STRENGTH: The ability of a fiber to retain its strength after being folded back and forth, commonly expressed as percent loss in breaking strength after flutter or fold testing.

GSM: Weight expressed in grams per square meter.

HAND: A subjective term for the way the fabric feels when touched. Terms like softness, crispness, dryness and silkiness all describe the hand of the fabric.

INITIAL MODULUS/MODULUS: A measure of a material's ability to resist stretch. Initial modulus is usually expressed as grams of load per unit stretch for a certain fiber denier. The higher the initial modulus, the less the fiber will stretch.

INSERT: A yarn or fiber laid directly into a fabric without first being woven or put into a scrim.

LAMINATE: Fabric constructed from layers of film, scrim and/or taffeta glued together under high pressure and/or heat to form a composite sail material.

PRIMARY YARN DIRECTION: The direction that is most resistant to stretch, typically due to a higher yarn count or a higher modulus fiber.

RADIAL: A panel layout where the seams and panels radiate from the corners of the sail in the direction of the highest load.

SAILMAKERS WEIGHT (SM-oz): Weight in ounces of a piece of fabric measuring 28.5" x 36".

SCRIM: A base fabric component created by laying out fibers in a grid pattern with the fibers joined at their intersection. A scrim can be constructed by passing fill and warp yarns over and under one another; by knitting, in which the fibers and "tied" at each intersection; or by laying the fibers straight across one another and connecting them at the intersections with glue.

TAFFETA: An unfinished fabric employed as a covering, usually in laminate sailcloth, often enhancing durability and chafe resistance

TENACITY: The tensile stress at rupture of a fiber expressed in grams of force per denier. Tenacity relates to the breaking strength of fibers and should not be confused with modulus, which relates more directly with a fiber's ability to resist stretch.

TENSILE STRENGTH: A measure of the ability of a fiber, yarn or fabric to withstand pulling stresses.

THREADLINE: The direction of the fibers or yarns in the warp, fill or bias.

UV RESISTANCE: A measure of the effect of sunlight on cloth. UV resistance is usually expressed as the time it would take for a material exposed to sunlight to lose half of its breaking strength.

WARP: The yarns or fibers in a fabric that run the length of a roll of cloth and, in a woven fabric, are interlaced with the fill (weft) yarns.

WOVEN: Material made by interlacing fibers over and under each other in a regular pattern. Types of weaves include plain, leno and basket, among others.

YARN: A continuous strand of fibers created when a cluster of individual fibers are twisted together. Yarns are used to create fabrics.