In comprehensive two-dimensional gas chromatography (GC×GC), samples experience two-dimensional separation implemented by a modulator which helps preserve the first-dimension separation and facilitates the second-dimension separation by periodically collecting, focusing and launching the material from the primary column onto the secondary column with a different stationary phase. Column overloading in GC×GC is a considerable problem, aggravated by the fact that two columns are involved. Broad first-dimension peaks of an analyte help produce smaller fractions of the analyte in the second-dimension, reducing the chance of secondary column overloading. One of the means to generate broad peaks in the first-dimension is to use thick film primary columns. A series of primary columns of various film thickness were tested in the study, and the results indicate that when other conditions are kept constant, 1μm film columns often provide better resolution in both first and second-dimension but at the expense of a much longer separation time; 0.1μm is clearly inadequate for GC×GC separation; 0.5 and 0.25μm film columns seem to be the best compromises.