Rubber bands are bands or closed rings made of rubber, which are used for closing packages or for holding together multiple loose parts. Hair bands, for example, are used to tie hair into a ponytail. Rubber bands are very stretchy. Depending on the application, they are manufactured in different diameters, widths and thicknesses. Rubber bands can be used as exercises bands in order to train the muscles to work against resilience. For household purposes, they are good for sealing air-tight preserving jars or closing plastic bags. They are also popular as a fastening device. On the one hand, they are easy to expand with physical strength, and on the other hand, they hold objects together well.