The lucky football fans who snagged tickets for the 2018 Super Bowl will venture inside the US Bank Stadium in Minneapolis, Minnesota on Sunday.

The stadium’s roof is also partially made of a special plastic film, which helps the interior remain a comfortable temperature during all seasons.

Business Insider spoke with Lance Evans, the venue’s lead architect, about the design.

Instead, the US Bank Stadium has a roof partly made of a plastic film called ethylene tetrafluoroethylene.

During the winter, the material gives natural sunlight to the field and helps the building store heat.

If the designers had used steel, the project would’ve cost $3 million more, according to Evans.

U.S. Bank Stadium