Explain why the below phenomenon occurs:

You have a sample of a fiber made of polyvinyl alcohol. To one end of the fiber, you tie a weight of 200 grams. Now you immerse the end tied to the weight in a beaker full of water such that only the weight and a portion of the fiber is immersed. To your surprise, the observation is that, as long as the weight remains suspended in water, a stable situation exists. But when the weight is rested at the bottom of the beaker, the fiber dissolves.