Sweater design is a specialization of fashion design in which knitted sweaters are designed to fulfill certain aesthetic, functional and commercial criteria. The designer typically considers factors such as the insulating power of the sweater (and its resulting warmth for the wearer); the fashion of its colors, patterns, silhouette and style lines, particularly the neckline and waistline; the convenience and practicality of its cut; and in commercial design, the cost of its production and the profitability of its price point. Sweater designs are often published in books and knitting magazines. Sweater design is an old art, but continues to attract new designers such as Nicky Epstein and Meg Swan

Criteria

The aim of sweater design is a sweater that fulfils certain criteria. The primary criterion is that its intended wearer wants to wear it and, in case of commercial sweater design, is willing to buy it at a commercially feasible price point. General secondary criteria include

• the insulating power, material and breathability of the sweater should make its intended wearer physically comfortable;

• the sweater should be appropriate for the occasion in which it will be worn;

• makes its intended wearer feel fashionably attractive;

To satisfy these secondary criteria, the designer has several tools at their disposal, such as yarns, colors, patterns, textures, necklines, hemlines, sleeve shapes, style lines, pockets and embellishments, as well as the fit of the garment to its intended wearer, the silhouette.

• For commercial sweater design, the production of the sweater must also be inexpensive, lest the price point be too high and make the sweater undesirable. This is generally done by simplifying the design so that it can be made by machine; more complicated commercial designs are generally hand-knit in pieces that are then stitched together. For example, the separate pieces of the hand-knit sweaters found in stores are generally knit and assembled in different villages in China.

Despite the wealth of design techniques and studies of successful designs, the primary criterion (that the sweater be desired) is not always achieved, often due to factors beyond the designer's control including serendipity.

Functional role as criterion

Sweaters are worn in various circumstances. For example, while some sweaters are worn at fancy dress occasions, others are worn to work, to religious services, in sporting or outdoors events such as hiking and camping. Similarly, the choice of a sweater can vary with different climates and different seasons, even with different times of the day. The sweater designer will generally target a particular occasion and temperature, e.g., a bulky, cabled, long-sleeved woolen seater for camping versus a refined, elegantly simple, short-sleeved cashmere sweater for white-collar work.

Comfort criterion

Comfort is paramount; the sweater should make the wearer feel at ease, in the most general sense. The temperature should be right, the fabric should "breathe" and should not irritate the skin. The sweater should hang right and not need constant adjustment; It should fit well and allow for customary motion without binding (e.g., at the armholes). Finally, a sweater should not make the wearer feel uncomfortable because of its "cut" (e.g. showing bra straps or too much cleavage) or general style (e.g., colors/patterns that the wearer feels are inappropriate).

Fitting a sweater

The fit of a sweater affects its comfort, its attractiveness and, sometimes, its practicality (e.g., dangling sleeves can fall into food or get caught on hooks).

The simplest sweaters (drop sleeve, cylindrical) require six measurements:

• circumference around the bust/chest (widest point)

• circumference (or width) of the neck

• under-arm length (armhole to sleeve-cuff hem)

• circumference of the arm at the sleeve-cuff hem

• back length (vertical distance from back of the neck to lower hem)

• armhole depth (vertical distance from bottom of armhole to lower hem)

A few more measurements usually produce a well-fitted sweater:

• circumference at the lower hem

• over-arm length (shoulder to sleeve-cuff hem)

• circumference of the upper arm near the armhole

• bust height (vertical distance from back of the neck to bust line)

• shoulder width (horizontal distance between bony shoulder points, measured across back)

For a more tailored look, even more measurements are necessary

• slope of the shoulders (vertical distance from base of neck to shoulder-point line)

• neck-shoulder length (horizontal distance from base of neck to shoulder point)

• circumference at the waist, the point of largest inward or outward curvature

• waist height (vertical distance from back of the neck to waist line)

Ideally, these measurements will be taken directly from the intended wearer, since bodies are idiosyncratic and these measurements may vary independently of one another, e.g., the bust measurement does not determine the waist or hip measurements, just as the height does not determine the arm length or shoulder width. Alternatively, the body measurements may be estimated from clothing that fits the wearer well. As a last resort, standard measurements such as EN 13402 or US standard clothing sizes may be used.

Of course, a sweater need not conform exactly to the wearer's body. Ease may be introduced to make the sweater larger than the body (oversized), typically by increasing the circumference measurements by 2-6 inches. Different amounts of ease can be introduced at different points to give the sweater a distinctive silhouette. For example, a "Gibson-girl" sleeve is produced by adding much ease to the upper arm and none to the lower arm, whereas the reverse is true for "bell" sleeves (also called "bishop" sleeves). Similarly, the bodice can fit loosely in the bust and tightly at the waist, or the reverse. Negative ease (i.e., subtracting from the body measurements) is also possible to achieve a very close-fitting look, but more than 2 inches is not recommended.

By making the sweater match the desired measurements, an excellently fitting sweater can be made. The width of a knitted piece at a given height should equal the corresponding circumference; for example, if the desired bust circumference is 38", then the front or back width at that height should be 19" each. The width of the upper sleeve (just before the sleeve cap, if any) should likewise equal the desired circumference of the upper arm.

Having determined the size and shapes of the knitted pieces, the number of stitches in a row is given by the desired width multiplied by the knitting gauge (e.g., 5 st/inch). Similarly, the number of rows in a column may be determined by multiplying the desired height by the vertical gauge (e.g., 3 rows/inch).