Some fabrics are soft and pliable while others take time to soften. Chemical processing such as starch or sizing, which are often added by the manufacturer to give the fabric a smooth finish and make it easier to handle, often creates stiffness. Other fabrics such as denim or canvas are naturally stiff and heavy. You can usually soften stiff, starchy fabric without much trouble, but read the care information first to be sure the fabric tolerates techniques such as machine or hand-washing, steam ironing, or tumble drying.
Make a simple, homemade fabric softener. Place about 3 cups of water in a quart jar, then add about a cup of apple cider vinegar and 1/2 cup of regular hair conditioner. Stir the mixture gently with a wooden spoon.
Fill a washing machine with warm water, then add about 1/2 cup of the fabric softener. Allow the fabric to soak overnight. If the fabric is delicate, wash it in a tub or basin with cool water and add 2 to 3 tablespoons of the fabric softener, then allow it to soak for 20 to 30 minutes.
Turn the washing machine on the rinse cycle to remove the fabric softener. If you washed the fabric by hand, rinse it in cool water. If the fabric is delicate, swirl it through the water with no agitation.
Tumble-dry the fabric on the warm setting, if appropriate. Otherwise, dry the fabric on the cool setting or hang it to dry, depending on the manufacturer's recommendations. Roll delicate fabrics in a fluffy towel to absorb excess water, then lay it on a dry towel to finish drying.
Wash and dry the fabric again if it still feels stiff.