Weave Definitions

Jon Soller
Soller Composites, LLC
Copyright 2004 – All Rights Reserved

I. Introduction

This paper explains the differences between common weave types, weave densities, and when they are best used. The first sections below briefly explain the weave types, followed by a discussion regarding when each weave type is generally best used. For more information, please contact us at info@sollercomposites.com.

II. General Weave Definition

Weaves are generally referred to and defined by a notation such as: 2X2, 4X4, and 3X1, for example. The first number in this set (e.g., the 3 in 3X1) refers to how many strands are crossed “over” before going “under” the perpendicular strands (in a 90-degree weave). The second number refers to how many strands are crossed “under” before going back “over” the perpendicular strands. That is, a 3X1 weave would run: over, over, over, under, over, over, over, under, etc. A 1X1 weave would run: over, under, over, under, etc.

III. Plain Weave

A Plain weave is defined as a 1X1 weave. Note the weave is over, under, over, under, etc.

IV. Twill Weave

A Twill weave is defined as a set of identical numbers both under and over (e.g., 2X2, 4X4). It creates the characteristic 45-degree diagonal look.

V. Harness-Satin Weave

A Harness-Satin (sometimes referred to as Harness, Satin, or Crowfoot) is defined as any number larger than 1 followed by X and a larger number. For example:

  • A 3X1 Harness-Satin is referred to as Harness-Satin 4, H4, or 4HS.
  • A 4X1 is Harness-Satin 5 (5HS or H5).
  • A 7X1 is Harness-Satin 8, H8, or 8HS.

In an H4 weave, the pattern runs: over, over, over, under, etc. There are exceptions—some Harness-Satins can be woven to resemble a 45-degree twill (e.g., a 3X1 looking like a twill is often called a 3X1 twill). However, an 8HS (even if it looks similar to a twill) is never referred to as a 7X1 twill.

VI. Choosing the Correct Weave Type

Each weave type has advantages and disadvantages. There is virtually no difference in fabric strength based on weave alone—choose based on aesthetics, curve complexity, and fabric weight needed for your application. (Note: Each fiber bend creates tiny strength variations, but these are generally negligible.)

  • Plain Weave (1X1): Tightest weave, least likely to fray. Best for flat/simple shapes where stability matters.
  • Twill Weave: Iconic 45-degree look, drapes better than plain (looser weave). A 4X4 twill drapes better than 2X2, but looser weaves fray more and may gap on curves.
  • Harness-Satin: Best drape for complex curves. Higher pic count (weaves per inch) improves conformity—an 8HS often outperforms twill even at similar pics. For extreme curves, 8HS is ideal; remove selvage if needed for better pivoting.

Most fabrics are 90-degree loomed (warp/fill). In general:

  • No complex curves + no aesthetics priority → Plain weave.
  • Aesthetics important → Twill (or sophisticated H7/H8 for premium look).
  • Very complex curves → 8 Harness-Satin.

VII. 1K, 3K, 6K – What Does It Mean?

The "K" refers to one thousand individual strands (filaments) per fiber bundle (tow). E.g., 3K = 3000 strands per bundle. At 12 pics/inch, a 3K fabric has 12 bundles per inch, each with 3000 filaments.

Typical weights: 1K ≈ 3.74 oz/sq yd; 3K ≈ 5.7 oz/sq yd.

Don't confuse tow size (e.g., 3K) with pic count (e.g., 12x12 pics/inch).

Carbon tow is untwisted (not yarn), so bundles vary in shape/thickness (flat to round). Approximate common dimensions (vary by brand/lot):

  • 3K tow: ~0.075" wide, ~0.001" thick (fairly flat).
  • 6K: ~0.12" wide, ~0.002" thick.
  • 12K: ~0.14" wide, ~0.006" thick.
  • 24K: ~0.36" wide, ~0.002" thick.

Special fibers like Hexcel IM series (IM7 etc.) are stronger/stiffer but "stripped" for performance—e.g., 12K IM7 may match common 6K dimensions/appearance for fabric consistency.

Please feel free to contact us for more info!

Soller Composites, LLC
Email: information@sollercomposites.com
(Updated contact from your site)

Last updated: March 2026