WHY SCARVES, AFGHANS AND SWEATER FRONTS CURL

As suggested in the introduction to this post, the first strand of the problem is caused by the desire of stockinette to curl: this desire is one of the most powerful forces in all of knitting. (For the reasons why this is so, click here.) When knit into a garment, such as a sweater, or a sleeve, sock, mitten or hat, the circular nature of the garment means that stockinette's curl is restrained by the garment's shape. This is due to the same forces as those which hold up stone domes or arches: the pressure from every side means that the tension inherent in the structure is evenly distributed. In stone arches, this even distribution of force means that the arch does not fall down. In knitting it means that when stockinette is restrained in a circular garment, the curling tension gets distributed around and around, so no one spot curls more than another.

Along an UNrestrained knit edge, however, such as the edge of a scarf, or the front or bottom bands of a cardigan, stockinette fabric will curl, regardless of what it is edged with. Of course, the problem is at its worst in a garment with two unrestrained edges: a scarf with wide garter stitch bands and only a very little stockinette in the middle will simply try to fold in half--the garter stitch edging itself isn't curling, but no matter how wide it is, the garter stitch band isn't preventing the stockinette in the middle from curling. Along a garment with only one unrestrained edge, a wide enough band will overcome the edge curl, but along a bottom band, "wide enough" might mean a bottom band 4 or 5 inches high, while along a front cardigan band, "wide enough" might take the front band to somewhere in the underarm region.

WHY CARDIGAN FRONT BANDS FLIP OPEN

The issue of curling is of course present in a cardigan front band. But this is not the reason why front bands want to flip open. Flipping, as opposed to curling, is due to a change in tension at the boundary between the stockinette fabric and the garter stitch or seed stitch band.

To explain: when first knit, the row count and the stitch count on garter stitch or seed stitch is smaller than that of the corresponding stockinette stitch (ie: of stockinette stitch knit on the same size needles). The explanation is not far to seek: the three-dimensional nature of these stitches means that more yarn is "sticking up" from the surface than is true of a stockinette stitch. Yet, the loop which creates the garter stitch is the same size--it is made around the same size needle--as the loop which creates the stockinette stitch just next to it. More "sticking up" with the same amount of yarn means something else has to be smaller, and each garter or seed stitch is smaller than a stockinette stitch in both width and length. In other words, because of its three dimensionality, each individual unit of garter stitch or seed stitch starts life shorter and narrower than each individual unit of stockinette.

Over the run of a front band, the smaller, tighter garter or seed stitch will "pull up" as compared to the stockinette stitch right beside it. A garter stitch or seed stitch band will basically want to turn inside out to relieve the pressure of being stressed all along the inside edge where it meets the stockinette stitch, while being relatively unstressed along the outer edge--the fabric edge. Usually, a cardigan front band cannot turn all the way inside out, because it is generally restrained along the top and the bottom edge by the top and bottom band. Usually, however, a garter stitch front band gets far enough along towards turning inside-out to flip open and stand at 90 degrees to the stockinette fabric beside it.

I should note that this tendency of garter stitch and seed front bands to flip open tends to lessen with time--so much so that on older sweaters, the originally tight and flipping garter or seed stitch band will now be seen gapping and sagging. You see, the unsupported edge of the front band--the fabric edge--will stretch out over time, as explained here and here. Also, the stitches will flatten as more yarn is drawn from the bouncy, springy texture to the connection between the stitches. This is another way of saying that garter and seed stitch tend to flatten as they age. As the pressure between the inside and the outside edges of the band equalize, there is less impetus for flipping. However, knowing that your sweater bands won't flip open five years from now is small consolation when they're flipping now.

WHY BOTTOM BANDS FLIP UP

As you know from experience, a line of purl will form a lovely crease horizontally upon a field of stockinette. This is the rationale behind knitting a "fold line" along the top of a sock or the edge of a hat brim. The top edge of a garter stitch bottom band acts a lot like a line of purl--the top line of garter stitch IS a purl line compared to the stocking stitch above it, and the second line of garter stitch, the one below the top line, wants to flip outward. Normally the outward and inward tension cancel one another, but as the stockinette Therefore, a garter stitch bottom band wants to fold along this line. While a purl row on stockinette will flip beautifully to the INSIDE, the thickness of a garter stitch border prevents the purl row at its top from flipping in, and this flip to the inside is further prevented by your body in the sweater But...the very next row down is ANOTHER purl line, relative to the row above it. Naturally, not being on a pure stockinette fabric means that the inclination to fold outward is somewhat weak, but nothing actually prevents this secondary fold line from flipping the way it wants to flip--outward. When this fault line inclined to fold outward is combined with an initially tighter row and stitch gauge, the flipping up of the bottom band is the result. Sit on a flipped up band once or twice, and the tendency is set.

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