Experimental and theoretical results on the flow pattern and film thickness of liquid falling films on the outside of a vertical pillow-type plate heat exchanger are presented. With the experimental setup, the wetting of a pillow plate and the local film thickness can be determined. The calculated mean film thickness is compared to literature data with an experimental investigation of a flat plate to assess the presented evaluation technique. Correlations for the mean film thickness on a flat plate and a pillow plate are given. The minimum flow rate per wetted length for a pillow plate is investigated.