The flag halyard used on Fritz Hansen chairs is made from 100% natural flax fibre with a core of nylon.
Vacuum the halyard on low to medium power to gather dust attached to the halyard.
If there are any spills or stains on the chair, remove them as quickly as possible by dabbing on the stain with a moist cloth. Avoid rubbing the halyard, as this can cause the fibres to draw out and leave the halyard damaged and worn.