Both types of directors owe fiduciary duties to the company. The exec directors are more involved because they are the ones running the day-to-day activities of the company. they are the ones who turn up every day and who work from 09.00 until 17.00 ( probably, in practice, much longer hours )
The non-execs attend meetings ( board meetings and sub-committee meetings ) in their capacity as “overseers” – checking that the execs are doing their jobs efficiently and effectively, acknowledging their responsibilities to the company, its stakeholders and their responsibilities to society at large