Modeling of vacuum based liquid composite molding methods (e.g. VARTM) relies on good understanding of closely coupled phenomena. The resin flow depends on the preform permeability, which in turn depends on the local fluid pressure; the preform compaction behavior, and the membrane stresses in the vacuum bag. To understand the nature of these coupled phenomena it is necessary to measure the preform thickness during the infusion and consolidation process. In a series of experiments the shadow moiré method was used to obtain a full field non contact measurement of a flat plate preform while silicone oil was infused under vacuum. The moiré interference pattern was recorded. A simple method was developed to calculate the change in preform thickness based on the differences between two moiré images and used to compare the mechanical behavior of the perform during infusion with similar behavior under loading in an servo-hydraulic testing machine.The perform deformation during compaction is noticeably different from that predicted from the mechanical tests, the possible reasons for this are discussed and a method of modeling this behavior is proposed.