In 1932, Dale Kleist tried to spray molten glass onto building blocks; the failed experiment created tiny fibres and helped make fibreglass insulation affordable

In 1932, Dale Kleist was trying to solve a practical problem with architectural glass blocks when his experiment produced an unintended spray of fine glass fibres. The attempt to seal the blocks failed, but the unexpected material offered a way to manufacture insulation-quality glass fibres in commercial quantities. Working with colleagues Jack Thomas and Games Slayter at Owens-Illinois Glass Company, Kleist helped develop a process that transformed the glass industry and made fibreglass insulation more accessible.

An experiment that went wrong

According to the National Inventors Hall of Fame, Kleist was working as a researcher at Owens-Illinois in 1932, after studying at Ohio State University. One project involved glass blocks used in buildings that needed to be sealed securely. Kleist attempted to spray molten glass onto the blocks to join their sections together. Instead of forming the seal he wanted, the equipment produced tiny, thread-like glass fibres. The result was a failure for the original task, but it caught the attention of Jack Thomas, who recognised that the fibres could help solve a different manufacturing challenge.


It was not easy to manufacture quality glass fibres at the time. Although earlier methods could produce glass wool, making insulation material at industrial scale was still difficult. Kleist's invention helped produce finer fibres, but it did not by itself create a marketable insulation product. Games Slayter, the engineer who had studied the technology of glass fibres, was also significant in this regard.

From accidental fibres to a commercial process

This was only the first step. With help from Kleist and Thomas, the process was improved to use steam to pull molten glass into thin strands. Steam provided an economical means of manufacture and the finer strands of glass wool necessary for insulation. There were practical challenges to overcome. Owens-Illinois had to come up with a feasible method of making the fibres without interfering with the company’s regular glass production. Company history mentions an experimental machine that exploded and caught fire, showing how difficult it was to move from laboratory discovery to industrial production. It required some additional improvements to enable a viable business.

One of the key moments was the formation of Owens-Corning Fiberglas Corporation by Owens-Illinois and Corning Glass on 31 October 1938. The company combined glass-manufacturing expertise with fibre technology and helped expand production and new applications. Kleist, Thomas and Slayter were honoured in the National Inventors Hall of Fame for their contribution to fibreglass technology.

Why the discovery mattered beyond the laboratory

Fibreglass insulation works by trapping air among a network of fine glass fibres, slowing the movement of heat through a building. The material can be installed in walls, roofs and other parts of a building to reduce heat transfer and help maintain indoor temperatures. Glass-fibre products have also been used in appliances such as stoves and refrigerators, as well as in industrial filtration and reinforced plastics.

The material could also be used to reinforce a range of products. Combining fibreglass with resins could strengthen plastics used in boats, cars and building materials. These wider applications came later and were not the immediate result of Kleist's original experiment. The 1932 incident marked an important step in the development of insulation technology. The failed attempt to seal the structural joints of the building blocks pointed to the possibility of creating fine fibres. Thomas recognised the potential of the discovery, and colleagues, including Slayter, helped develop the technology for glass-fibre insulation.