Superglass Holdings, the glass fibre insulation products manufacturer, said yesterday that underlying trading for the year to 31 August will be “slightly” below expectations. It also said net debt has increased to £17.7m in an update following its year-end. Sales were ahead of the forecast in cured products, compensating for further underperformance in some blowing wool product lines. Market weakness and cost pressures have hit margins, it added. Capital expenditure increased after a furnace failure last year, for which the insurance claim has yet to be fully settled.