University of Richmond LawProf Kevin Walsh writes:

The hat is a custom-made replica of the hat depicted in Holbein’s famous portrait of St. Thomas More. It was a gift from the St. Thomas More Society of Richmond, Virginia. We presented it to him in November 2010 as a memento of his participation in our 27th annual Red Mass and dinner.

 

I kinda see the resemblance.

H/T Michelle Olson

Update: Walsh talks to ABC News:

To find that answer, ABC’s Sarah Parnass spoke with Scalia’s former clerk, Kevin Walsh.

Walsh, who now teaches at University of Richmond School of Law, said the association of Catholic lawyers to which he belongs, St. Thomas More Society of Richmond Va., presented Scalia with the hat in 2010.

The hat is a replica of one worn by St. Thomas More in his most iconic portrait, done by Hans Holbein, according to Walsh.

When giving Justice Scalia the hat, the members of the St. Thomas More Society thought it would be a nice memento. “If nothing else it would be suitable for university functions,” Scalia said.

Walsh said the significance of Scalia’s wearing the hat likely doesn’t go beyond function. In the past, Scalia has worn a skull cap, much like the one Justice Breyer sported today. But the skull cap doesn’t have earflaps – the More hat does.

“That one’s warmer,” Walsh said, comparing the hat Scalia wore today with the one he wore to the 2009 inauguration. “I’d say it’s more functional.”