Tunnel trays are equipped with tunnels arranged either in parallel or crosswise to the flow direction. The elongated vapor risers are covered by slotted caps. Shape and number of the slots in the caps are variable as in the case of bubble cap trays. Trays with tunnels in parallel to the flow direction suit medium to very high liquid loads. Trays with tunnels crosswise to flow are appropriate for very low liquid loads and provide long residence times.
They can be manufactured also from thermoplastic materials like bubble cap trays.