The Bishop Andrewes cap is a recent reinvention of the ancient style of academic cap as part of academic dress

Academic dress

Academic dress or academical dress is a traditional form of clothing for academic settings, primarily tertiary education, worn mainly by those that have been admitted to a university degree or hold a status that entitles them to assume them...

 before it developed into the modern mortarboard as it is known today . The cap is named after Bishop Andrewes who may have not have worn this style of cap at all.

The cap is similar to the mortarboard save that it does not have a hard board to stiffen the top square. Instead, it is soft and floppy. Instead of a tassel

Tassel

A tassel is a finishing feature in fabric decoration. It is a universal ornament that is seen in varying versions in many cultures around the globe.-Etymology:...

 and button

Button

In modern clothing and fashion design, a button is a small fastener, most commonly made of plastic, but also frequently of seashell, which secures two pieces of fabric together. In archaeology, a button can be a significant artifact. In the applied arts and in craft, a button can be an example of...

, there is a tump or pompom of silk at the centre of the apex. It is usually made of black velvet.

The cap is currently prescribed for the full academical dress of DD

Doctor of Divinity

Doctor of Divinity is an advanced academic degree in divinity. Historically, it identified one who had been licensed by a university to teach Christian theology or related religious subjects....

s at Cambridge University as well as the official dress of certain learned societies such as The Burgon Society.