Why is steam formed when ironing a line-dried shirt

Why is steam formed when ironing a line-dried shirt  

We often generate steam when ironing clothes made of cotton. The steam forms even if the cloth previously felt dry. But the steam is only formed if the shirt was dried outside, e.g. on a clothes line. We see no steam if the shirt was dried on a radiator before ironing. 

Anyone who irons a lot will also notice how the texture of the cotton changes following ironing beforehand, the cotton felt coarse and somewhat starched, but afterwards it feels more pliable and softer. 

Water (in the form of vapour) sticks readily to many surfaces. 

Substances partition preferentially during adsorption, leaving the gaseous or liquid phases and forming a new layer on the surface of a substrate. 

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