Technical Guide

Yarns for Socks / Jeans

New DuPont Type 403 Elastic Yarn in Sock Bodies for Improved Comfort, Fit, and Shape Retention


New from DuPont Research

New from DuPont ResearchType 403 elastic yarn is a member of the Type 400 series, an entirely new class of elastic fibers for apparel developed by DuPont research. These revolu­tionary new fibers are direct-use yarns that require no texturing or covering. They are specially designed to deliver superior performance and aesthetics in appli­cations that require low to moderate stretch.


Compared to the textured stretch yarns currently in use, Type 403 provides greater, more durable stretch and recovery, and a softer, smoother handle. This new development in elastic yarns provides manufacturers with an exciting opportunity to upgrade virtually any sock offering that currently uses textured yarns.

Figure 1. Comparison of stretch and recovery of selected stretch yarns

Elongation (%)


Figure 2. Micrographs of DuPont Type 400 Series

As-Spun After Crimp Development


Table 1: Knitting comparison of socks with textured yarns and DuPont T403. Less stretch yarn is required with Type 403 to achieve the same cross-stretch and length stretch as with textured yarns.



Type 403 Processing Information
Companion Fibers

Type 403 elastic yarn is suitable for use with virtually any primary yarn now in commercial use, including cotton, nylon, polyester, and acrylic.


• Creel packages of Type 403 in the typical plating yarn location on the knitting machine. Type 403 is torque-free, so there is no need for alternating “S” and “Z” twist courses. • Handle packages with care. Avoid denting package shoulders or otherwise damaging packages during handling. • The first yarn guide should be directly in line with the center of the yarn package, and at a sufficient distance to ensure smooth yarn takeoff (Figure 4). • Keep the number of contact points between the first yarn guide and the knitting head to a minimum, and avoid sharp angles. • Keep all contact points free of burrs, grooves, or other surface defects.

Figure 4. Creeling.

Knitting Type 403 is plated with the primary yarn and knit into every course of the sock body. It may be plated to the outside, the inside, or in a sandwich construction. Type 403 can be run on high speed machines over a range of needle counts in single or double cylinder knitting machines.


Knitting tension for Type 403 may be slightly higher than for textured yarns. However, no special tension devices are required; conventional disk tensioners with light springs can be used with Type 403.


The thermal shrinkage of Type 403 is about 5 to 7%. Stitch length may have to be adjusted accordingly. The greige cross-stretch should be 2 to 2.5 cm (0.75 to 1.0 in.) greater than the desired finished cross-stretch, depending on construction.


Dyeing Type 403 is disperse dyeable to deep shades at temperatures up to 130°C (266°F), or may be dyed to lighter shades at 100°C (212°F). An after-scour is recommended for optimal washfastness.


When Type 403 is combined with cotton, union dyeing can be achieved with a two-bath dye process. Disperse-dye the Type 403 first and follow with a reductive after-scour. Then dye the cotton with reactive or direct dyes.


Boarding Socks with Type 403 may be boarded by conventional steam or pressure steam boarding. Typical boarding-Conditions are from 121 to 132°C (250 to 270°F) for 1 to 3 minutes. The boarding performance of Type 403 is comparable to that of conventional textured yarns (see Figure 5).

Typical Properties


Yarn Size

83, 120dtex 75, 110 denier


3.3 g/dtex (3.7 g/denier)

Crimp Potential


Recoverable Stretch


The Product

Type 403 is a multicomponent yarn in which different polymers are joined together within each filament. When exposed to heat, each polymer shrinks to a different degree, producing a smooth helical crimp. Because the crimp is not mechanically induced, the stretch and recovery properties of Type 403 are greater (Figure 1), and significantly more durable, than those of textured yarns. One feature that ssets Type 403 apart from other yarns is the regularity of the developed crimp (Figure 2). It is this regularity that accounts for the unique handle of socks containing Type 403.

A New Class of Elastic Fibers

Type 403 is the DuPont trade name for one of an entirely new class of elastic fibers. The U.S. Federal Trade Commission has temporarily assigned the generic designation “DP 0002” to this new class of fibers. Internationally, the new fibers are identified as “elastic fibre”.

A key requirement for a fiber to be classified as DP 0002 is that the fiber must exhibit inherent (not mechanically induced) recoverable stretch of at least 35% upon loading with 185 mg/dtex and unloading to 5.4 mg/dtex.
Features of Type 403

• Greater and more durable recovery power than textured yarns

• Excellent chemical and UV resistance

• Excellent hand, different from that of textured yarns

• Direct-use yarn


For sock manufacturers, the comparatively high stretch and recovery of Type 403 can result in improved yarn yield. Table 1 compares Type 403 with textured polyester stretch yarns in a typical sock construction. Note that a smaller amount of Type 403 provides more stretch (extended length) than the textured yarn, with virtually identical sock layout (relaxed length).


Figure 3 illustrates the durability and chemical resistance of Type 403. It shows the effect of laundering with detergent and chlorine bleach upon recovery force retention in sock bodies made with Type 403 and textured yarns. The figure clearly shows that sock bodies with Type 403 will retain more of their original shape and power after repeated consumer laundering than those with textured yarns.

Figure 3: Effect of laundering upon recovery force retention in socks

Low cylinder vacuum produces the best stitch clarity. For regular terry constructions, the vacuum should be on for the heel and toe only; it should be off for the boot and foot. For sandwich terry and flat-knit constructions, the vacuum should be on for the entire sock.


Wet Finishing Crimp Development Type 403 develops its crimp at its first exposure to wet or dry heat during the fabric finishing operation. The following conditions are required for complete crimp development: • Minimal tension upon the fabric • Wet heat at 60 – 130°C (140 – 266°F), or… Dry heat at 160 – 170°C (320 – 338°F) Conventional sock processing methods are sufficient to fully develop the stretch potential of Type 403.


Bleaching Type 403 is resistant to both hydrogen peroxide and chlorine bleach, and is suitable for existing bleaching processes. Hydrogen peroxide tunnel processes typically expose socks to temperatures of about 82 to 93°C (180 to 200°F) with a residence time of about 40 to 60 minutes. These conditions are more than sufficient to allow Type 403 to fully develop its crimp.


For vat processes, a bleach bath ratio of 20:1 is recommended.


Chlorine bleaching does not harm Type 403, but if you plan to put elastane in the sock-top, be sure to consult Technical Bulletin L521: LYCRA9 T162B: Chlorine-Resistant Performance for Athletic Sock Tops.


Figure 5: Boarding performance (conventional boarding) of three plating yarns in cotton socks knitted on single-cylinder electronic machine

Textured  Textured DuPont
Nylon Polyester Type 403

Decitex (denier)

Number of Filaments

Package Size kg (Ib)

Tube Core Length cm (in.)

Inner Tube Diameter cm (in.)

83 (75)


2.7 (6.0)


7.6 (3.0)



2.7 (6.0)


7.6 (3.0)

Use of the LYCRA® Brand

Licensed manufacturers may use the LYCRA® brand and icon on socks with Type 403 if the following criteria are met: • Type 403 must be knitted into every course of the sock body • Minimum Type 403 content in the sock body is 10% • LYCRA® brand elastane fiber must be present in the sock top • LYCRA* must be the only elastane present in the sock


For more information, contact your DuPont representative.

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As always, count on DuPont to provide unmatched technical support for your development efforts when you use DuPont yarns for apparel.