You can stretch a cowboy hat yourself at home. But, taking your hat to a skilled hatter to lengthen it out and enlarge the cap by a full size without distorting its shape is ideal. The material it is composed of and the type of hat you have will determine the optimal stretch. Organic materials in caps can cause slow shrinkage with time, particularly if washed. Humidity, sweat, and weather play a role in the shrinking of the hat.