Australian Public Service Commissioner Peter Woolcott told Senate estimates on Monday the pandemic - which forced tens of thousands of public servants out of their offices - actually improved how the Commonwealth bureaucracy worked.

"It's actually led to some real improvements in terms of how we work as a public service, the concept of one enterprise, breaking down silos and working flexibility at home at scale and the IT systems held up," Mr Woolcott said.

Assistant commissioner of strategic policy research, Katrina Purcell said a working group representing 65,000 workers found no dip in productivity, despite the large number of people working from home.

The volume of work carried out in some areas increased by more than 50 per cent, as the public service dealt with the ever-evolving crisis.

There was a slight decrease in leave and an increase in part-time work and overtime, Ms Purcell said.

The number of unscheduled absences fell from 3.1 days per worker to 2.3 days in the period between April and June.

"That's a quarter decrease. That's quite a significant decline in unscheduled absences," Ms Purcell said.

The fall was likely due to people self-isolating, as well as the increase in flexible working arrangements, Ms Purcell said.

There was also a 19 per cent improvement on internal communication from the year before, while the number of public servants who felt inspired to do new or better things increase by 17 per cent.

However Mr Woolcott was concerned the benefits would not last.

"We do well in a crisis but what always concerns me is sustainability over a long period of time," Mr Woolcott said.

"This is not going away, COVID-19 and this crisis, at least until we get a vaccine so that's the first question I have. The second question is what is the value in terms of working in an office, the collegiality, the ability to bounce ideas off people, the networks you develop."

Currently around 28 per cent of public servants were working exclusively from home, compared to 22 per cent working flexibly pre-COVID-19.

However, it would be impossible for all staff to return to the office due to social distancing restrictions, Mr Woolcott acknowledged.

He said it was likely there would be some kind of hybrid model going forward, where public servants would work part of the week in the office and the remainder from home.

The public service commission told department secretaries in March staff members needed to start working from home "as soon as practicable" amid concerns from unions, politicians and staff about the risk of the virus spreading through offices.

The commission revised its advice last month, saying public servants in areas where there was limited or no transmission of coronavirus should go back to the office with restrictions in place.