Box pleat

A pleat (older plait) is a type of fold formed by doubling fabric back upon itself and securing it in place. It is commonly used in clothing and upholstery to gather a wide piece of fabric to a narrower circumference.

Pleats are categorized as pressed, that is, ironed or otherwise heat-set into a sharp crease, or unpressed, falling in soft rounded folds.

Pleats sewn into place are called tucks.

A vertically hanging piece of fabric such as a skirt or a drape will often be described in terms of its "fullness." Fullness represents the thickness/ depth of the pleats in relation to the original width of the fabric: fabric sewn at "zero fullness" would actually be flat and have no pleats; fabric sewn at "100% fullness" is pleated so that it takes up exactly half as much width as it would if it were not pleated at all (i.e., 24 inches would be pleated down to 12 inches); if sewn at "150% fullness," the unpleated fabric would be two and a half times wider than the final pleated piece (i.e., an unpleated 30 inches would end up as 12 pleated inches of fabric: 12+1.50(12)=30); if fullness were to be "50%", the original fabric would be one and a half times the width of the pleated (i.e., 18 inches of width would end up as 12 pleated inches: 12+0.50(12)=18), etc.

Accordion pleats or knife pleats are a form of tight pleating which allows the garment to expand its shape when moving. Accordion pleating is also used for some dress sleeves, such as pleating the end of the elbow, with the fullness of the pleat gathered closely at the cuff. This form of pleating inspired the "skirt dancing" of Loie Fuller. Accordion pleats may also be used in hand fans.

Box pleats are knife pleats back-to-back, and have a tendency to spring out from the waistline. They have the same 3:1 ratio as knife pleats, and may also be stacked to form "stacked-" or "double-box pleats". These stacked box pleats create more fullness and have a 5:1 ratio. They also create a bulkier seam. Inverted box pleats have the "box" on the inside rather than the outside.

Cartridge pleats are used to gather a large amount of fabric into a small waistband or armscye without adding bulk to the seam. This type of pleating also allows the fabric of the skirt or sleeve to spring out from the seam. During the 15th and 16th centuries, this form of pleating was popular in the garments of men and women. Fabric is evenly gathered using two or more lengths of basting stitches, and the top of each pleat is whipstitched onto the waistband or armscye. Cartridge pleating was resurrected in 1840s fashion to attach the increasingly full bell-shaped skirts to the fashionable narrow waist.

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Wikipedia