The Ayrshire mill embarked upon a planned maintenance shutdown in mid-March, which was then extended due to the Covid-19 pandemic.
The mill was restarted on 20-21 April.
A spokesman said: “We can confirm that our Caledonian Paper Mill had been standing still due to extended maintenance which has been prolonged in light of the corona situation.
“It’s worth pointing out in that context that we have met customer demand at all times, relying on our global network of modern paper mills and flexible planning approaches.”
Caledonian Paper makes LWC magazine papers and has an annual production capacity of 250,000 tonnes.
The site has a biomass combined heat and power plant, a single paper machine, a debarking plant, and a pressurised groundwood mechanical pulp mill. It employs 290 staff.
Helsinki-headquartered UPM said that its Q1 results had not been materially impacted by the Covid-19 pandemic. Sales fell 15% to €2.29bn “due to lower pulp and paper prices and lower deliveries of graphic papers”.
EBITDA declined by 26% to €279m.
President and CEO Jussi Pesonen commented: “Many of our products serve essential everyday needs and may therefore see relatively solid demand during the pandemic, particularly for pulp, speciality papers and self-adhesive labels. On the other hand, the demand for graphic papers, plywood and timber is likely to be impacted by the lockdowns and the following global recession.”
UPM said it was planning to use shift arrangements, temporary layoffs, or reduced working hours as required to adjust its operations in different scenarios due to the virus crisis.