Why does jersey curl but rib does not?

Jersey is a single knit with different front and back faces, and the imbalance makes the edges roll. Rib alternates knit and purl columns symmetrically, so the forces balance and the fabric lies flat, which is why cuffs and hems are ribbed.

Which stretches more?

Rib knit, especially across its width. Its knit and purl columns pull together and open out, giving strong crosswise stretch and recovery. Jersey stretches too, but less, and mainly along its length.

Why are cuffs and collars ribbed?

Because rib's crosswise stretch lets a cuff expand over a hand or head and then spring back to hug the wrist or neck, and because rib lies flat without curling, so it makes a clean self-finished edge.

Side by side

Jersey vs Rib Knit

Jersey and rib knit are the two foundational knit structures, and the difference is in how the stitches are arranged. Jersey is a single knit, all the stitches facing one way, so it is smooth on the front, looped on the back, light, and only modestly stretchy. Rib knit alternates columns of knit and purl, which pull together into raised ribs that give powerful crosswise stretch and a fabric that looks the same on both faces.

Jersey

No. 067

weft knit, stockinette · first documented Middle Ages

Rib Knit

No. 157

alternating columns of knit and purl stitches · first documented Middle Ages

The differences

Aspect	Jersey	Rib Knit
Structure	A single (plain) knit; all stitches face the same way.	Alternating columns of knit and purl stitches.
Faces	Different front and back: smooth V's one side, loops the other.	The same on both faces, with vertical ribs.
Stretch	Stretches, but modestly, and mostly lengthwise.	Strong crosswise stretch and recovery; springs back.
Edges	Curls at the edges, which is why hems are needed.	Lies flat and does not curl; ideal for unhemmed cuffs.
Typical use	T-shirts, dresses, the body of most knitwear.	Cuffs, collars, waistbands, and close-fitting garments.

Which to choose

Jersey is the smooth, light, everyday knit that makes the body of a t-shirt; rib is the stretchy, reversible, non-curling structure that finishes its cuffs and collar. Most knit garments use both, jersey for the body and rib for the trim.

Common questions

Why does jersey curl but rib does not?: Jersey is a single knit with different front and back faces, and the imbalance makes the edges roll. Rib alternates knit and purl columns symmetrically, so the forces balance and the fabric lies flat, which is why cuffs and hems are ribbed.
Which stretches more?: Rib knit, especially across its width. Its knit and purl columns pull together and open out, giving strong crosswise stretch and recovery. Jersey stretches too, but less, and mainly along its length.
Why are cuffs and collars ribbed?: Because rib's crosswise stretch lets a cuff expand over a hand or head and then spring back to hug the wrist or neck, and because rib lies flat without curling, so it makes a clean self-finished edge.

Full entry: Jersey Full entry: Rib Knit

Sources & References

1.Jersey (fabric), Wikipedia
2.Knitting, Wikipedia
3.Ribbing (knitting), Wikipedia
4.Knitted fabric, Wikipedia