Knitwear stretches, sags, pills and shrinks in ways that woven garments do not, and all of it comes from the same structural fact.
Loops, not grids
A woven fabric is threads crossing at right angles, held by friction and tension. It has very little give unless the fibre itself stretches.
A knit is a single yarn looped through itself, continuously. Pull it and the loops elongate; release and they recover, up to a point.
Which is why knits are comfortable and why they deform. The structure is designed to move.
Past a certain extension the loops do not recover, and the deformation is permanent.
Gauge
The number of stitches per unit width, which determines how fine the fabric is.
Fine gauge produces thin smooth fabric that layers well. Chunky gauge produces thick textured fabric with more air trapped and more insulation.
Fine gauge also shows every construction fault, since there is nowhere for irregularity to hide.
Neither is better. They are different fabrics with different uses, and a fine gauge jumper will not keep you as warm as a chunky one regardless of fibre.
Fully fashioned against cut and sew
The distinction that separates good knitwear from the rest.
Fully fashioned means each panel is knitted to shape, with stitches added or removed to create the curve of a shoulder or an armhole, then the panels are linked together.
Cut and sew means a flat length of knitted fabric is cut to shape and stitched, exactly like a woven garment.
Cutting a knit severs the loops, which is why cut edges must be secured and why they eventually unravel or roll.
Fully fashioned garments show small marks where the shaping occurred, usually a few inches in from the shoulder seam, and those marks are the sign to look for.
Linking
How the panels are joined.
Linking joins loop to loop by hand or on a linking machine, producing a flat seam that stretches with the fabric.
Overlocking joins with a serged seam, which is fast and creates a bulky ridge that does not stretch at the same rate as the panels.
Which is why some jumpers feel comfortable at the shoulder and others have a rope running across it.
Why shoulders sag
Hanging a knitted garment loads the entire weight through the shoulder loops, continuously, for months.
Those loops elongate and do not recover.
Folding is the only correct storage, and this single change prevents most knitwear deformation.
Where hanging is unavoidable, folding the garment over the bar rather than putting it on the shoulders distributes the load through the whole fabric.
Shrinkage and felting
Wool shrinks because the scales on the fibre surface ratchet against each other under heat and agitation, locking permanently.
This is felting and it cannot be reversed.
Superwash wool has had the scales removed or coated, which prevents it, and it also changes the handle and reduces some of the fibre's natural properties.
Cold water, minimal agitation and drying flat prevent the problem entirely with untreated wool, which is what the care label is trying to communicate.
Blocking
The technique that recovers shape and almost nobody uses.
Wet the garment, lay it flat, and gently ease it to its correct measurements, then leave it to dry undisturbed.
The fibres set in the shape they dry in, which means a stretched jumper can frequently be brought back substantially.
Measuring the garment when new and noting the figures makes this far easier later, and it takes two minutes.
The cashmere question
Cashmere quality varies enormously and price is a poor guide.
Fibre length and fineness are what matter. Short fibres pill immediately and the garment looks tired within a season.
Two-ply yarn — two strands twisted together — is more durable than single ply and is generally disclosed.
A useful check is to stretch a section gently and release. Good cashmere springs back. Poor cashmere stays stretched, and it will do the same at the elbows within weeks.
Ribbing and where it matters
The alternating knit and purl columns at cuffs, hems and necklines.
Ribbing pulls in laterally because the columns fold against each other, which is what creates the elastic grip.
Deeper ribbing grips better and holds shape longer. A single inch of ribbing at a cuff will relax within a season.
Some ribbing includes a fine elastic thread, which extends the life considerably and eventually perishes, at which point the cuff goes permanently slack.
Neckline construction
The place a jumper looks worn first.
A neckline that stretches out has usually been finished with a band that lacked either sufficient depth or sufficient tension.
Pulling a jumper over the head repeatedly loads the neckline more than anything else does, and unfastening the top button of a shirt underneath before removing it genuinely helps.
Moths again, since it is knitwear that suffers
Protein fibres are what they eat, and knitwear stored for a season is the classic loss.
Damage appears as small irregular holes, generally in clusters, and frequently in areas that were soiled.
Storing clean, in sealed containers, with cedar or lavender as a supplement rather than a primary defence, handles most of it.
Small holes can be darned invisibly on knitwear more easily than on woven fabric, because the loop structure can be reconstructed with matching yarn.