Linen sheets have natural fibers that will soften as they are used and washed. It just takes time and patience for this to naturally occur. Some linen sheets come from the manufacturer softened, this process is called stone washing. If you are struggling with being patient for your sheets to get softer, you can add a teaspoon of baking soda to the laundry detergent in the washing machine, vinegar to the rinse cycle or use wool dryer balls in the dryer.