Each piece of clothing sold has a care label, which lists recommended cleaning methods for the clothing. For a sweater, the instructions might say to machine wash the sweater using a gentle cycle, and then tumble dry at a low temperature. They might say to hand wash the sweater in cold water and lay the sweater flat to dry. The label might even say, “Dry clean only.”

Figure 1  You can use the care labels on clothing to sort laundry into batches for cleaning. The care label shown is for a wool sweater that needs to be dry cleaned or washed by hand.

Why is it necessary to put care instructions on a label? The same cleaning method will not work for all materials. For example, a shirt made from 100 percent cotton may need to be ironed after washing. But a shirt made from a cotton and polyester blend may come out of the dryer wrinkle free. A wool jacket often needs to be dry cleaned because wool can shrink when washed in water.

The tendency to wrinkle when washed is a property of cotton. The tendency not to wrinkle when washed is a property of polyester. The tendency to shrink when washed is a property of wool. Cotton, wool, and polyester have different properties because they have different compositions. The word composition comes from a Latin word meaning “a putting together,” or the combining of parts into a whole. Based on their compositions, materials can be divided into pure substances and mixtures.