The backscattered form function of an infinite cylinder becomes very small at a certain value of thickness for values of the dimensionless frequencyka<1. This phenomena is examined by deriving the equations of motion in terms of the overall mass and compressibility of the cylinder within a thin shell approximation. The value of the form function is determined for the most part by the first two terms in the normal mode expansion. These two terms are of comparable magnitude. Additionally, each of these two terms is shown to depend primarily on either the mass or compressibility of the cylinder. Cancellation of these two terms occurs at the value of thickness for which the backscattered form function is very small.