Shirt material has fewer folds when the arm is straight than when the arm is bent. When the arm is bent at the elbow, the shirt gathers and bunches up at the inside of the arm but is pulled at the underside of the arm.
The characteristics of a pair of pants are similar to shirts because they are also influenced by the pull of gravity, the body’s form and the light illuminating the subject.
Observe how the body’s form underneath affects the outer shape of the shirt. Notice that the shirt’s form is different where it is in contact with the body compared to where it is away from the body.
The light source as well as the body’s form underneath influence the values of the shirt.
With the straight leg, the material hangs down, making little contact with the body. For the bent leg, the material bunches up behind and below the knee.
With values added, the folds and form of the pants have a more realistic appearance of depth.