A shirt collar has no bones in it. It is cloth, and yet it stands up, folds over at a predictable line and keeps two symmetrical points. The reason is a third layer that never appears in a product photograph: a fusible interlining, a thin web with heat-activated adhesive on one side, pressed between the two outer layers under heat and pressure.
Two pieces, not one
A collar is cut as a band — the part that rises from the neck — and a separate fall, the part that folds down. Cutting them separately lets the fold be placed by the pattern rather than by ironing. It also lets the two pieces use the grain differently: the band needs to resist stretching around the neck, while the fall needs to lie flat and turn a clean corner at the points.
The interlining is usually cut slightly smaller than the outer cloth, so it stops short of the seam allowance. If it ran to the edge, the turn of the cloth would show a hard ridge from the outside. The softness of a collar edge is a decision about where one layer ends.
The roll is engineered
Where the collar folds is not arbitrary. A softer interlining in the band and a firmer one in the fall, or a second small piece at the points, sets how high the collar stands and how wide the fold rolls. A dress collar that must sit under a jacket behaves differently from a casual one meant to stay open. Both can be made on the same sewing line; the difference is a different piece of interlining.
The points get their own attention. A small triangular insert, or a few extra stitches holding the layers together, keeps a point from curling up after washing. Without it the two layers shrink by slightly different amounts and the tip slowly turns over.
Why it blisters
The familiar bubbles that appear on an old collar are a failure of the bond, not of the cloth. Cloth and interlining shrink at different rates when wet and warm; the adhesive was applied as a pattern of tiny dots precisely so the laminate could still move a little. Repeated washing, high heat in a dryer, or a press that was too cool on the day the collar was made can break that bond in patches. Once a patch lets go, the outer layer lifts and the bubble is permanent.
This is the hidden cost of a very stiff collar. The tighter the bond and the heavier the interlining, the cleaner it looks on day one — and the more visible any local failure becomes. A softer collar ages less dramatically because it asks less of the adhesive.
What to look at
Hold a collar up to the light and see whether one layer seems to end just inside the edge. Run a finger along the fold: it should roll, not crease. Then press the points flat and let go. A collar is a small laminate, and its whole behaviour is decided by the layer you cannot see.