Glass, stainless steel infuser. Not suitable for microwave or dishwasher. Clean using gentle detergent and avoid abrasive sponges. Ensure flask is clean and dry before being stored.Your new flask is made of glass - handle with care! Avoid dropping your flask and be gentle when opening, closing, inserting and removing inner parts to prevent mechanical shock.Avoid exposing your flask to drastic changes in temperature by allowing it to slowly change into room temperature first (e.g don't take your flask out of the fridge and pour in boiling water) to prevent thermal shock.