When clothes get shorter but not narrower

Short answer: Knit fabric shrinks most in length because the loops pull together vertically. Width often stays the same. That is why t shirts get short, not narrow.

The loops pull together

The structure of a knit allows the most movement in height, because each individual loop can pull together vertically without changing the width much. This is the same mechanism that makes a new sweater shrink, and it applies to almost any knitted fabric. See bamboo t shirt for women.

Heat triggers it

Hot water and the tumble dryer are the two triggers, because heat makes the fibers contract and the loops tighten. Cold washing and air drying remove most of the problem, even on materials otherwise known for shrinking easily. See bamboo clothing for women.

Most of it happens in the first wash

Fibers settle in the first wash, where the biggest jump in length usually happens all at once. After that the change is small, and a garment that survives the first wash without trouble usually keeps its shape for the rest of its life. See bamboo underwear for women.

Stretch it while it is damp

A damp garment can be gently stretched back into length, because the fibers are more forgiving while not fully dry. Lay it flat on a towel, pull gently at the shoulders and hem, and let it dry in the new shape. See bamboo tops for women.

The tumble dryer is the biggest culprit

The heat from a tumble dryer is far stronger than from the washing machine alone, and this is often where the final shrinkage happens. Avoiding the dryer entirely for knitted items keeps most of the original length intact over time.

The quality of the knit matters

A tight, even knit shrinks less than a loose knit, because the loops have less room to pull together. A cheap, loosely knitted garment can therefore shrink noticeably more than a pricier alternative in the same wash.

Sizing up cannot fix a shrunk t shirt

If you buy a larger size to compensate in advance, you just get a garment that is too wide from the start. The fix lies in the wash temperature, not the size choice, if you want to keep the original fit.

Check for moisture before hanging it up

A garment that is still very wet pulls together more easily under its own weight while hanging to dry. Press it gently in a towel first, so less water needs to evaporate while it hangs.