"If necessity is the mother of invention, then for the glass fiber industry, adversity is the father."
    — William Boeschenstein, Owens-Corning Fiberglas, 1995

The world’s largest bottle plant stood empty. Prohibition and the Depression had crushed the demand for bottles. American bottle maker Owens-Illinois needed a new product. There might be an enormous market for insulation made of lightweight glass fibers, but no one had found a way to mass-produce fibers that were fine enough.

Owens-Illinois tried drawing fibers by using air and steam, but failed to produce anything thinner than broom straws. Then in 1932, a lucky accident happened. Dale Kleist, an intern engineer, was using a metal-layer gun—sometimes used to bronze baby shoes—to try to generate a stream of glass to fuse two halves of a glass block. Instead of a stream, the jets of air coming from the gun produced an explosion of fine, lightweight fibers.

Kleist’s frustration was Owens-Illinois salvation. His “experiment” showed that air or steam, applied at a critical angle, can stretch glass into very fine fibers. Within months, Owens-Illinois had converted the disused bottle plant into a factory for manufacturing fiberglass wool insulation.

Like cotton candy

It looks a lot like making cotton candy—but the modern rotary method for making glass wool insulation took much longer to perfect. Like the confectioner’s process, it uses centrifugal force to rapidly transform a viscous liquid into fluffy fibers.

German inventors Fritz Hager and Friedrich Rosengarth patented a method in 1929 that used centrifugal force to mass-produce glass fiber. A stream of molten glass fell onto a rotating disk and was spun off as droplets that trailed long filaments. The filaments were fairly fine, but they clung to the disk’s drive shaft and had to be sawed off.

In the 1950s, Owens Corning and France’s St. Gobain refined and combined the rotary method and the blowing process. As glass passed through holes in the rim of a rotating disk, a blast of hot air further stretched the filaments, making them even finer and more lightweight. This fast, efficient method continues to meet an ever-growing demand. Fiberglass insulation was once rare. Today, it’s rare to find a new American home without it.

How fine is fine?

Glass fibers have ranged from the early broomstraw-size to the nearly-invisible microfiber used in the Apollo mission’s spacesuits. One of the early fibers would have made over 6,000 of the microfibers. It would take more than 1,200 microfibers to equal the size of a human hair.

Flexible as silk

A glass dress? The mere thought drew crowds of people to Chicago’s Columbian Exposition in 1893. They had hoped the dress would be transparent. It wasn’t. And it was barely wearable. Its glass fibers broke when they were bent or rubbed, so the dress was prickly. If glass fibers were to be as flexible as silk, they would have to be a lot finer.

German innovator Oscar Gossler tried drawing finer fibers in 1908, pulling them over a drum from streams of melted glass that emerged from holes in a vat. The trouble was that the corrosive glass eventually enlarged the holes, and the fibers became coarse.

By lining the holes with corrosion-resistant platinum and using high-quality glass, Owens Corning produced fiberglass filaments so fine that they were flexible enough to be spun into thread. Today, the thread is used not for clothing but for making industrial fabrics and adding strength and durability to many plastics.

The Corning Museum of Glass
This article was originally published in Innovations in Glass, 1999, pp. 58–59.

Published on October 20, 2011