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E-glass fiber glass yarn is different from other continuous (non-insulation) products, in that generally, the binder on the yarn (applied when forming the glass fiber) is not compatible with a polymer resin and the packaging is much different from that of glass fiber products made specifically for reinforcing plastics.  Most all yarn binder systems are starch-oil systems (> 90%), designed primarily for protecting the yarn in the weaving process.  Starch oil systems are also used on yarns made for texturizing and in unidirectional tape and reinforced paper applications. In respect to packaging, fiber glass yarn is offered on bobbins or beams.

In the weaving application it is critical that the yarn is protected while being woven, hence the starch-oil. Since most of the woven fabric ends up in a polymer composite application, the fabric must be made resin compatible. This is done, by the weaver, by burning the starch oil from the fabric (heat cleaning) and then applying a resin compatible binder to fabric.  The majority of the composite applications for fiber glass woven yarn are in the high pressure laminate market (printed circuit boards).

Besides being categorized by binder type, the yarn is further delineated by filament diameter and yield. The most popular yarn types are produced from of a “G” (9 micron) filament size and in yields of 3700, 7500, and 15,000 yards per pound (in metric nomenclature, respectively 134, 66, and 33 TEX*). Filament diameters offered in fiber glass yarn will range from a “BC” (4 microns) through to a “K” (13 micron) and yields will vary between 1800 to 180,000 yards per pound (276 to 2.75 TEX). Note, fiber glass roving is generally offered in the “J” to “U” filament size and yields of 103 to 1800 yards per pound (11 to 24 micron and in TEX counts of 4800 to 276).

Fiber glass yarn is always twisted and sometimes plied. Fiber glass yarn is twisted in either an “S” twist or “Z” twist (the direction of the twist) and can be offered in a plied form as well (multiple ends). In general, single yarn strands are offered in “Z” twist in 0.5 & 1.0 turns per inch (20 & 50 turns per meter). Plied yarns are offered in an “S” twist with the most popular plied yarns offered in either 2.8 or 3.8 turns per inch (112 or 152 turns per meter). One creates a balanced “S” twisted plied yarn by using a “Z” twist singles yarn. See product nomenclature examples below:

ECG-75 1/0 0.5Z (EC9 – 66 1x0  Z20)  means electrical grade continuous glass fiber with a “G” filament size, 7500 yards per pound, and 1 end with a .5 Z twist (metric nomenclature in parentheses).

ECDE-150 1/3  2.8S (EC6 – 33  1x3  S112) means electrical grade continuous glass fiber with a “DE” filament size, 15000 yards per pound, 3 yarn ends plied together to make one end with a 2.3 S twist.  Note, in this example the plied yarn yield (three ends) becomes 5000 yards per pound.

Yarn binder systems, other than starch oil, of note are resin compatible and plastisol compatible. Generally both are woven as well. For instance, Parabeam use plastic compatible yarn to weave a 3-D fabric. The plastisol compatible yarn is coated with a plastisol prior to weaving into items such as window screening.


Filament Diameter References:

Letter Designation

























*TEX = grams per 1000 meters


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