Which of the following items should not be worn under a dry suit?

Wearing cotton clothing under a dry suit is not advisable due to its moisture-wicking properties. When wet, cotton absorbs water and holds it against the skin, leading to a loss of insulation and increasing the risk of hypothermia. In cold water or underwater environments, staying dry and maintaining warmth is crucial for the diver's safety and comfort.

In contrast, other materials like neoprene, fleece, and wool are better choices for thermal insulation. Neoprene provides buoyancy and warmth, fleece is lightweight and retains heat, and wool can effectively wick moisture away while still providing insulation even when wet. Therefore, avoiding cotton and choosing appropriate undergarments is critical for an optimal dry suit diving experience.