Answer:
High density and molecular weight
Step-by-step explanation:
Polymers are typically huge structures of smaller structures which are bonded to each other by covalent bonds. These smaller structures are also known as monomers. Since all of the monomers, typically thousands of monomers, are bonded together in one structure and not present as separate molecules or ions, this effect produces a close packed structure with a greater density similar to those seen in metals.
Due to high density and high molecular weight, polymers are solid as a result.