A rigid closed cell polyisocyanate-based foams is created by reacting at least one organic polyisocyanate with compounds having at least two active hydrogen atoms in the presence of an n-pentane blowing agent. The methods generate uniform proliferated populations of cells. The method and apparatus can dynamically join virtual circuits to the bundle and remove them as needed, allowing the bundle to grow and contract according to traffic demands. The length of each slot is substantially equivalent to a length of the housing.