It was a custom-built model constructed by Matte Paintings supervisor Matt Jefferies. He used various materials including:
* Wood for the basic structure
* Plastic for details
* Metal for certain accents
* Paint for the final finish
Jefferies's design was groundbreaking for its time, and became iconic. It is now considered a classic of science fiction design.
While model kits of the Enterprise have been available since the original series, none were used in the actual filming.