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Sure, ethylene tetrafluoroethylene (ETFE) sounds like a word Mary Poppins would invent, but the material will likely be an integral part of the new NFL stadium projects looming on the horizon in Chicago, Nashville and Buffalo.

ETFE is a type of tensile membrane — synthetic, weather-resistant material stretched over an open span — that is increasingly being used on all parts of stadiums, most notably as a more cost-effective replacement for domes or retractable roofs. Awareness of ETFE has grown significantly in recent years thanks to its use on the roofs or canopies of U.S. Bank Stadium, SoFi Stadium and Allegiant Stadium. And at least one of the teams building a new stadium, the Tennessee Titans, is planning to enclose their proposed new stadium with an ETFE covering to enable year-round events, including basketball.  

These days, “if a building is going to have a roof on it in some way, it’s going to have ETFE on it somehow,” said Dan Wacker, Mortenson director of preconstruction.

Innovation around man-made polymers like ETFE and its cousin, PTFE (full name: polytetrafluoroethylene, also known by the brand name Teflon) has gone on full blast for over a century, but creative designers and engineers are just beginning to cook up their own custom formulas for use in sports venues, too.  

“It’s like a platform that you can innovate on,” said Phil Kolbo, Populous principal and senior architect. “You’re not pulling things off the shelf anymore; you’re making what you need.”   

Tensile membranes are lighter — and cheaper — than steel, allow controlled natural light into otherwise dim indoor stadiums and have an open-ended potential for use in all parts of a building — not just roofs but in place of glass windows, or as coverings over premium areas or seating bowls. The latter concept could also work in a place like Buffalo, which doesn’t want to surrender its late season home-field weather advantage and has already committed to an outdoor stadium, but could keep direct snowfall off its fans with a tensile canopy system encompassing the field.  

“When you talk about the fan experience on open-air facilities, traditionally NFL stadiums haven’t had canopy coverage,” said Wacker. “But Europe is full of these PTFE roofs that shade the fans, MLS is going for 100% coverage of its fans, and I think the NFL would look at teams using that as an option.”    

Tensile systems can be stretched over two sides of anything: a backyard, a premium bar in a stadium or a sports venue’s roof. The flexibility of tensile materials allows designers to incorporate complex curves and shaping that would be impossible, or at least very costly, with traditional steel and metal panel roofs, according to David Peragallo, sales and specification manager, Americas, at French firm Serge Ferrari Group.  

“[Tensile fabrics] give architects and designers of sports stadiums a unique freedom of form and flexibility to take their design to the next level,” Peragallo wrote in an email to Sports Business Journal.

TFE materials are highly resistant to heat and sunlight abuse, are hydrophobic, and have a low coefficient of friction, meaning they’re easy to clean because nothing sticks to them. ETFE is thinner than PTFE, allows natural light into a space and is better for fully enclosing and conditioning a building; PTFE is more effective for shading structures, like canopies, because it’s a mesh and not as transparent.  

Tensile materials like ETFE are lighter than traditional roofs and need less support. That’s critical for stadium project budgets, because the longspan steel propping up a roof can run 600 to 800 feet in length and is the most expensive part of the stadium, according to Wacker. The cost of a fully steel-supported roof, especially if it mechanically retracts, is the reason so many NFL stadiums don’t have them.  

U.S. Bank Stadium in Minneapolis was one of the first major venues in the U.S. to have an ETFE roof in 2016. The Vikings wanted a retractable roof, but Kevin Taylor, principal and sector manager, venues, for architecture firm HKS, said that the ETFE alternative gave the Vikings “retractability” without the price of a retractable roof, saving roughly $100 million.  

“We spent a lot of time making sure we could get a lot of natural light coming into that facility,” said Taylor, who was the lead designer on AT&T Stadium, U.S. Bank Stadium and SoFi Stadium. “Once we did it on the Vikings, I knew it was going to happen on other projects.” 

ETFE and related materials are also lighter than glass, making them practical for vertical use, like on the concourse at Globe Life Field in Arlington, or AT&T Stadium across the street, where they ultimately settled on PTFE.

Where U.S. Bank Stadium is fully enclosed, SoFi Stadium is a canopied venue, like a stadium perched beneath a single-layer ETFE “carport” held in place by extensive cabling. U.S. Bank Stadium’s roof entailed a three-layer pillow system (the sheets of ETFE are inflated), whose ambient heat helps melt snow off the roof in the winter. 

Allegiant Stadium also used a pillow system, which is critical for keeping out ultraviolet and infrared light and enabling the venue to meet building code. That’s one of the challenges of working with ETFE, said Kolbo. But frit, a pattern or ink imprinted on a material, can also help deter UV or infrared that would otherwise pass through ETFE. And new products are already coming to market that possess low-e coatings to block infrared rays just like a much heavier pane of glass could. 

Future versions of ETFE will likely incorporate (not just house) LED and collect solar energy. Those enhancements will be made in the lab, but designers are already expanding the tensile fabric palette for sports venues, like at Allianz Field where Populous and Kolbo worked with engineers from Walter P Moore, Geiger, and Pfeifer to create a custom type of PTFE material specifically for the 93,540-square-foot façade wrapped around Minnesota United’s stadium.

“We didn’t go, ‘oh, that’s a cool material, let’s use that,’” said Kolbo. “We said ‘hey, this is what we want to do. We want reflection, we want lamination, we want to see through it. These are the things that we want; let’s make it.’”

Bret McCormick can be reached at bmccormick@sportsbusinessjournal.com.

First NFL sportsbook opens in AZ; MLB preps for on-field changes; Saudi Arabia eyes World Cup '30 bid

NFF’s Steve Hatchell on what’s next after amazing start to college football season With so much happening around college sports off the field, it seemed almost too much to hope that the opening weekend of football season would live up to expectations. “Finally, we got to cheer for our teams,” said Steve Hatchell, CEO of the National Football Foundation, in an SBJ Spotlight interview looking at the college football landscape. “There was some great attendance at games … some real excitement and just some terrific games. I’m hoping that this type of enthusiasm goes on for the entire year.” Hatchell talked with SBJ’s Ross Nethery about the big stories in college sports and what might come next. On the CFP expansion to 12 teams: “Football is played in all 50 states … and we work with all 774 colleges and universities around the country. So if we can have a playoff that reflects on the investment in coaching and on the players from around the country, I think that’s for the betterment of the game.”

With opening week quickly approaching, Ben Fischer, Reggie Walker, and Xavier Hunter were joined by Jabari Young of Forbes to preview the upcoming NFL season. Topics discussed included the Deshaun Watson suspension, Denver Broncos ownership, Dolphins owner Stephen Ross, and the league’s advancements in media.

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