Final answer:
The tunica media is the layer consisting of elastic and collagenous fibers that is thicker in veins, aiding in the return of blood to the heart, although arteries have a generally thicker wall overall.
Step-by-step explanation:
The layer made of elastic and collagenous fibers which is thicker in veins is the tunica media. For arteries, the tunica media is generally the thickest layer and is abundant in elastic fibers and smooth muscle tissues that help regulate the diameter of the vessels through vasoconstriction and vasodilation. Arteries have thicker smooth muscle and connective tissue to cope with higher pressures but in veins, the tunica media is thicker compared to the tunica intima.
Veins have a thicker tunica media layer than arteries to help them propel blood back to the heart against gravity. This is aided by the contraction of surrounding skeletal muscles and the presence of valves to prevent backflow. However, overall, arteries have thicker walls than veins due to the need to accommodate higher pressure.