Viruses are composed of nucleic acid genomes and interior proteins that are surrounded by a protective protein shell called a capsid.
Instead of making the capsid out of one giant protein, viruses typically utilize many identical copies of the same protein that combine together to form this outer shell. This way, the virus can be economical, using one gene repetitively to make many small proteins instead of devoting a large portion of its genome to making a large protein coat.
When making your paper container, you may have found a shape that uses several triangles to enclose the yarn and cotton balls, which represent a virus's nucleic acid and interior proteins, respectively. The majority of viruses are composed of triangular protein sub-units that associate to form an icosahedron—a 20-sided shape. This shape helps the virus to minimize its surface-area-to-volume ratio, which allows it to carry the most genetic material and internal proteins inside a given protein shell.
One way to categorize viruses is by whether or not they are surrounded by a membrane, called a viral envelope. A large number of viruses that infect humans have envelopes, including HIV, the virus that causes AIDS. You can place your capsid into the plastic bag to model these enveloped viruses.
Coronaviruses, such as the one that causes COVID-19, also have envelopes. Unlike HIV, they have helical interiors, which is another common shape for viruses.