The companies will show off the space apparel later in the year.
VSS Unity during an April 2018 test flight.
For Virgin Galactic astronauts, the answer to the question of "What does one wear in space?" will be Under Armour.
That means both spacesuits and boots, as well as uniforms for those back on Earth, according to a blog post from the companies Thursday.
"The custom-fitted Under Armour spacesuits will inspire confidence through comfort and practicality without compromising the natural desire of every Virgin Galactic astronaut both to feel good and look good during this unparalleled life experience," the post said.
The full line of space apparel will be out later in the year, in advance of Virgin Galactic's first commercial flight.
In December, Virgin Galactic's SpaceShipTwo space plane, the VSS Unity, skimmed the edge of space (at 51.4 miles, or 82.7 kilometers) during a crewed test flight.