I want to say this book was published anywhere from the 80's to the early 2000's. I believe the portal was in the desert in the US, and the government built a facility around it. Objects from the portal/hole/doorway were unlike any technology/substance known to humans. The only specific object I remember was a super dense material, perhaps cloth like, that was incredibly heavy because of its density. The portal was one-way.
I found it!! (Well, a kind stranger on reddit found it). The Breach by Patrick Lee. More of a thriller with sci-fi vibes. Thanks everyone for the help!
Thirty years ago, in a facility buried beneath a vast Wyoming emptiness, an experiment gone awry accidentally opened a door. It is the world's best-kept secret-and its most terrifying. Trying to regain his life in the Alaskan wilds, ex-con/ex-cop Travis Chase stumbles upon an impossible scene: a crashed 747 passenger jet filled with the murdered dead, including the wife of the [P]resident of the United States.