Why is it so much easier to iron a crease into a shirt than iron it out again?



As title please

In: Physics

Because there’s no easy way to “invert” a crease in fabric. You can’t get flatter than flat.

When you iron the crease in, you’re folding the crease through 180 degrees. When you try to iron it out you’re opening both “legs” up 90 degrees to each side then trying to press it flat. So a lot more stress went into the bend to set the crease than you can put in to remove it.

When you iron a crease “into” a shirt – you are basically bending and folding the fabric at a certain place – and the “bend or fold line is visible” as a crease. Folding and pressing it with a hot iron – sort of – seals the fold and makes it semi – permanant (i.e. until you uncrease it). In other words – you commit that crease / fold shape to the memory of the fibers at that location.

When you are uncreasing it – you are flattening the fold out and making the “fold line” disappear. This works well if you try to iron the shirt on a very firm and lightly padded surface – you will be able to unfold the line pretty well (but not 100%). That is because fabric threads retain their creased shape – as if its imprinted in their memory.

The best option to remove a crease is to wet that fabric at the crease location, let the thread fibers become soft and pliable (lose their crease memory) and then iron them with a hot iron to imprint new “uncreased” memory state onto it.

(An alternative answer. The other answers are much more accurate) A crease is any fold greater than 0 degrees and less than 180(since it cant fold through itself) and flat is 0 degrees so the probability that you get a crease is 1/181. Getting a 0 degree crease would have the same probability as getting a perfect 90 degree crease.