Director Lenny Abrahamson has revealed the mystery of why Michael Fassbender wears a fibre-glass head throughout his new film Frank.

Publicity shots issued from the set of the film in New Mexico this week show the Killarney actor 'with a head on him' next to Maggie Gyllenhaal and Domhnall Gleeson.

"The character Michael plays is so agoraphobic he has to wear a big, fake head.

"So he kind of takes his room with him whenever he goes outside," explained Lenny.

The Irish Film Board has invested half-a-million euro into the tale of an avant-garde band, based on the memoirs of journalist and filmmaker Jon Ronson, and are getting their money's worth by the sound of it.

"It's set in Ireland, England and the States, but we're shooting both the Irish and English scenes in Ireland," said Lenny.

Which will be a lot warmer than New Mexico, where filming started last week.

"It's been freezing all week. Michael was glad of the head," producer Ed Guiney told The Diary.