Electric car maker Tesla just added a new option for its Model S sedan: a glass roof.

The roof can give passengers the feeling of “an open expansive cabin,” said the company on its website. Tesla CEO Elon Musk said in a tweet that the new roof, which will cost an extra $1500, makes the Model S car interior “feel amazing.”

The move is another example of how Tesla continues to add new features and technology to its four-year old vehicle, the second to debut in its growing lineup. In particular, Tesla has routinely updated the Model S with technology that has also been available in more recent car models.

For example, the company’s upcoming fourth car, the Model 3, will come with a glass roof.

Earlier this year Tesla TSLA upgraded the Model S’s front fascia and grill to look more like the company’s third car the Model X.

For more on why SolarCity really needs the Tesla deal to go through watch our video.

The new glass roof option also shows off Tesla’s new investment in automotive glass technology. Earlier this week Musk revealed that the company had created an automotive glass division.

In the tweet on Friday, Musk said that the Model S glass roof was “very hard to develop.”

Some of that automotive glass tech will also be used to help create Tesla’s solar roof product, which incorporates glass laid on top of solar films, with a solar cell underneath. Musk said that the glass part of the solar roof makes it more durable than a standard roof.

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The new glass car roof feature is also the latest of a steady stream of announcements for Tesla over the past few months.

The company is acquiring sister solar company SolarCity SCTY . The shareholder vote on the controversial merger is planned for Nov. 17.

In the face of a substantial amount of skepticism, the companies are both making efforts to paint as positive a picture of their companies as possible. Critics contest that SolarCity’s debt and spending could weigh down Tesla’s own major spending and aggressive growth plans.