Ductwork Connectors & Flexible Duct Connectors

In buildings of all kinds, the ducts that circulate air for heating and cooling are usually connected to HVAC machinery by flexible duct connectors made out of durable fabric. For many decades, textiles woven from asbestos fibers were the primary material for this application.

Years Produced: 1938–1980s

Metal air ducts are commonly used to connect all the rooms in a building to its heating, ventilation and air conditioning (HVAC) equipment. However, when ducts are attached to heaters, air handlers and air conditioners directly, the noise and vibrations produced by this equipment may rattle throughout the entire ventilation system.

Construction workers can prevent this problem by installing a flexible duct connector between the machinery and the ductwork. These connectors must be able to both absorb constant vibrations and resist hot and cold air circulated by HVAC systems, ideally lasting as long as the HVAC system itself.

For several decades during the mid-20th century, manufacturers thought asbestos to be the ideal material for flexible duct connectors. Naturally occurring asbestos fibers are durable and practically fireproof, yet flexible enough to be woven into fabric, and they could be sourced cheaply from North American mines.

Once the dangers of asbestos exposure became well understood by the American public, manufacturers began to use other materials for flexible duct connectors. Unfortunately, however, many old buildings still contain degrading asbestos materials, and the tradesmen who worked with these materials in the past bear the risk of developing asbestos-related diseases in the present.

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At a Glance

  • Places Used: Heating, ventilation and air conditioning systems for buildings

  • Toxicity: High

  • Asbestos Use Banned: No

  • Friable: Yes

Manufacturers began testing asbestos duct connectors as early as 1938, when the Johns Manville Corporation published about their advantages in the American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) Journal. In 1951, as air conditioning systems were starting to become popular and affordable for homes, the National Fire Protection Agency officially recommended asbestos for flexible duct connectors.

Some duct connectors were manufactured as simple strips of coarse fabric woven from nearly pure asbestos yarn, which were secured to metal duct joints by clips or rivets. More sophisticated duct connectors were coated with rubber or vinyl to provide a more air-tight seal.

As almost all American industries phased out the use of asbestos during the 1970s and 1980s, manufacturers began to switch to cotton canvas or fiberglass mesh for flexible duct connectors.

Manufacturers of asbestos duct connectors included:

Dangers of Asbestos Duct Connectors

During the height of American asbestos use, flexible duct connectors commonly contained 50 to 100 percent chrysotile asbestos.

The factory workers who produced these connectors suffered the worst asbestos exposure, followed by the construction tradesmen who installed, repaired or removed asbestos duct connectors on a regular basis. Occupational asbestos exposure is the primary cause of diseases such as asbestosis and pleural mesothelioma.

Furthermore, aging and constant exposure to temperature extremes can cause duct-connector material to become friable, or easily crumbled into inhalable dust. Over time, even rubberized or vinyl-coated asbestos duct connectors can deteriorate to the point of releasing asbestos fibers into the air.

Microscopic asbestos dust has no scent, and exposure generally does not cause symptoms to develop until years later. Because duct connectors are perfectly positioned to affect all the air in a building, degrading asbestos duct connectors pose a serious asbestos exposure risk.


Many people who develop asbestos-related diseases after years of working with toxic duct connectors are able to receive compensation by holding manufacturers liable in court.

For example, in 2005 a retired sheet metal worker named Genaro Garcia won a lawsuit against Duro Dyne. Garcia had been exposed to asbestos in Duro Dyne’s flexible duct connectors throughout his 48-year career, never having been advised to wear respiratory protection, and he had gone on to develop peritoneal mesothelioma in 2002.

A San Francisco jury awarded him nearly $2 million to cover his pain and suffering, lost earning capacity and medical expenses — including the costs of two years of chemotherapy treatments.

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Matt Mauney

Matt Mauney is an award-winning journalist with nearly a decade of professional writing experience. He joined Asbestos.com in 2016, and he spends much of his time reading, analyzing and reporting on mesothelioma research articles to ensure people in the mesothelioma community know the latest medical advancements. Prior to joining Asbestos.com, Matt was a reporter at the Orlando Sentinel. Matt also edits some of the pages on the website. He also holds a certificate in health writing from the Centers for Disease Control and Prevention.

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