Original: Blankets were traditionally made of wool because of wool 's warmth , breathability and natural fire-retardant properties , while sheets were made of cotton or linen , which are less irritating to the skin . Nowadays , synthetic fibers are frequently used for both .
Simplified: Blankets were traditionally made of wool because it is warm , naturally fire-retardant , and allows air to circulate well , while today synthetic fibers are frequently used .