The soft, broken-in feel of a well-loved T-shirt is a wonderful thing. So wonderful, in fact, you're looking for a way to obtain that comfortable softness without the wait. In truth, age is the only surefire way to get that lived-in feeling from your tee, but you can experiment with a handful of methods to reduce the stiffness of a newer T-shirt before it becomes a vintage classic.
Washing your T-shirts repeatedly with a commercial fabric softener is an easy way to soften them up for a comfortable wear. Fabric softener works by coating the threads of your garment with a lubricating chemical sheath that makes it feel softer to the touch, while causing it to be less prone to wrinkling and static cling. One drawback: some people find fabric softener to be a skin irritant.
Putting your T-shirts in the dryer to tumble dry is another effective way to soften up clothing -- in this case, by prematurely aging it. The mechanical action of tumble drying abrades the fibers of your tee -- just like normal wear and tear does -- only faster. If you don't mind the wear, you can break in your T-shirts by running them through a few extra tumble-dry cycles on low to medium heat. Tumble drying does increase the risk of shrinkage, especially with 100-percent cotton tees.
A salt brine can soften your T-shirts to a certain extent, acting as a natural fabric softener. Dissolve a half-cup of salt into a quart of water and soak your tee in the mixture for three days, then wash with a small amount of detergent and tumble dry. This method is not as effective as commercial fabric softeners and the results may be subtle, though still noticeable.
Use vinegar as a fabric softener. Add a half-cup of white vinegar to the rinse cycle of your washing machine in the same way you would use a commercial fabric softener. You can also try using a fabric-softener dispenser ball in the washer but this time filled with vinegar. Your laundry will not smell like vinegar, but your shirts will be a little softer to the touch.