Not only 3-section umbrella frames are used in umbrellas, they are commonly used in parasol too. The canopy on parasol is coated with special coating to block UV light. These coatings are quite thick and make an umbrella much heavier. Thus it is often used in 3-section frames not 5-section as it is easier to fold an UV coated 3-section parasol. UV umbrella is often used in summer to block sunlight and protect one’s skin.