Some newer washing machines have a steam cycle, which uses hot water vapor to better clean and flatten your laundry right inside the wash basket.
The steam cycle on a washer works similarly to a garment steamer. The hot air from the steam causes the fibers in your fabric to relax, gently smoothing out wrinkles and creases. Steam cycles increase the temperature of your wash, which also helps provide a deeper cleaning when washing clothes that are stained or heavily soiled. The higher temperatures in the steam cycle can also help sanitize your clothes and reduce allergens. Keep in mind that heat can cause clothes to shrink, so be careful of using a steam cycle on clothes made of cotton, wool or other fabrics known to shrink.