Look on the bottom of a recyclable plastic bottle - chances are you will see a PE or PS which means polyethylene or polystyrene. These materials are examples of what happens to polymers when they solidify: the chains are entangled and packed together to make light, tough, flexible materials.
A way to think about some of these materials is to think of what a big glob of cooked spaghetti is like. If you stretch it a bit, it is kind of elastic, but if you really pull hard, the noodles start to slide past one another and the whole glob starts to permanently deform. At least that is the idea! Does this remind you of what happens to a PE plastic bag when you stretch it? Think about what must be happening to the microscopic spaghetti that the bag is made up of!
If you heat up PE or PS to moderate temperatures, if the chains have not been chemically stuck together (`cross-linked') they will melt, and turn into goopy liquids, which are called polymer melts. Some polymers are melts even at room temperature, like polydimethylsiloxane (PDMS), or poly(ethylene-propylene) (PEP).
Remembering that paper is made of cellulose, which is a polymer of biological origin, if you look around the room that you are in, you will see that a good fraction of the stuff in it is made of polymers. And of course, you are, too!
John Marko, marko@msc.cornell.edu