the face fibres made of polypropylene are a manmade fibre and have zero water retention so any excess water will pass through the carpet into the backing. this is the problem, but it doesn't shrink, IT GROWS or more exactly it swells.
this cuases shrinkage because the polypropylene fibres wrap around the the swelling fibres, the swollen fibres are now bigger so the faces fibres have to travel a greater distance, because they are a set length they cannot do this so they pull in. Which shows its self as a shortening of the carpet.
once the carpet dries the swelling will go back, so sometimes the carpet will return back to its normal size, so don't kick it back until it is completely dry
hope this makes sense
