In Star Trek IV: The Voyage Home, what futuristic material does Scotty give to a 20th-century engineer?

In Star Trek IV: The Voyage Home, Scotty gives a 20th-century engineer transparent aluminum as a futuristic material.

Scotty trades the formula for transparent aluminum to Dr. Nichols, who is developing materials for a large tank. The scene takes place in 1986 San Francisco, after the Enterprise crew travels back in time to obtain humpback whales.

The material is fictional in the film, but the idea was inspired by real materials research. Transparent aluminum is commonly used as the name for aluminum oxynitride, a transparent ceramic developed for tough optical applications. Real transparent ceramics are not simply ordinary aluminum metal made clear.

A common mix-up is confusing this material with Star Trek's fictional alloys, such as duranium or tritanium. The film specifically names transparent aluminum, and Scotty's exchange is one of the franchise's best-known examples of technology being brought from the future into the past.