Start with the care label
Remove loose debris gently and check the care instructions before applying any cleaner. Test an allowed product in a discreet area. Do not assume a removable cover can go into a washing machine.
For appropriate Sunbrella upholstery
Sunbrella’s general upholstery guidance describes mild soap and water, thorough rinsing and air drying. Follow the instructions for the exact material and consult the cushion maker before removing a casing.
Dry before enclosing
Allow the whole cushion, including its insert, to dry before storing it or covering the furniture. A dry surface alone does not prove the inside is dry.
Material reference: Sunbrella upholstery care guide. Use the guidance for your exact material and construction.