Antique telephone insulators are glass or porcelain caps that were originally designed to insulate telephone wires from the wooden poles that held them. The manufacturing of telephone insulators peaked from the 1920s to the 1940s, and the antique insulators are now a popular collectible.
The insulators were produced in a variety of shapes and colors, including amber, cobalt blue, olive green and purple, although clear and aqua are most common. Value is affected by shape, color and condition, although most insulators are common and have little monetary value. Some insulators are embossed with a manufacturer's name and style number. Antique telephone insulators can be found at flea markets, antique stores and online auctions.