The most commonly used thread used to sew shade sails are a blend of polyester and cotton. While these threads are UV stable, typical life expectancy in a shade sail application is between 2 and 5 years depending on the amount of stress.
Thread strength drops by up to 50% over this time due to exposure to UV – the bigger the sail the higher the stresses. The higher the sail is stressed the quicker it will fail.
High performance sails are made using a PTFE thread which costs 10 times the price of a comparable poly-cotton blend. PTFE threads loose less than 20% of their strength with UV exposure over a 10-15 year period.