Girth is all about expansion. The elasticity of the penis tissue can only expand when it is brought into a state of "beyond" maximum expansion. When you think of how tough the tunica tissue is, with less than 5% elasticity, it is easy to do the math to breakdown this tissue and force it into new growth. Adding and stress beyond the 6% range of "normal expansion" will result in a deformation of tissue allowing for gradual, permanent expansion. Your goal in girth should always be getting beyond your natural, erect, girth measurement. Pumping will aid in expansion but much of this expansion comes from fluid. Although the extra fluid will eventually drain that skin stretch it provides does prime for natural girth exercise. Slow Squash Jelqs are a great way to reach the desired state and pumping may even help in maintaining this state.