Summary Spraying of MDI-based products is a common practice for many workers. The application of spray foam to insulate commercial or residential buildings is one example. During such applications, workers are exposed to MDI aerosols. MDI is a known chemical sensitizer that can cause occupational asthma. To minimize occupational exposure to MDI, the workplace environment must be monitored to map areas containing residual MDI and identify sectors and tasks where improvements in prevention are required. The current mapping of some workplaces is not as precise as it should be, mainly because the filter sampling devices used are unable to detect MDI with precision. Filter-based sampling systems (that is, solvent-free systems) such as Iso-Chek® and OSHA Method 47, underestimate real exposure levels and permissible sampling times are too short. With bubbler sampling systems, on the other hand, there is a risk not only of exposure to solvents (used in the bubblers) but also of explosion or fire as well as bubbler breakage or overflow or evaporation to dryness of the absorbing solution. A more effective sampling device could improve field evaluations. The purpose of this project was to identify optimal testing conditions, in the laboratory, using the CIP 10-M sampler, and to compare the CIP 10-M and ASSET™ EZ4-NCO samplers with a bubbler sampling system during the application of polyurethane foam insulation. An alternative solution using a personal microbiological sampler (CIP 10-M) was investigated for sampling MDI during the application of foam insulation. The aqueous collection fluid normally used with the CIP 10-M was replaced by a non-volatile cosolvent into which the derivatization agent 1-(2-methoxyphenyl) piperazine (MOPIP) was introduced. When the CIP 10-M is in operation, air containing MDI aerosols is aspirated through its air inlet and enters the rotating cup containing the cosolvent. The aerosols are driven by centrifugal force onto the cosolvent, where they dissolve and are immediately stabilized by the MOPIP. The method’s linearity range is 0.8 to 26 ug/m3 in air, assuming 60 minutes of sampling at 10 L/min. Comparative sampling was performed in a real MDI foam spraying environment with CIP 10-Ms, bubblers containing toluene/MOPIP (reference approach) and ASSET™ EZ4-NCOs. The results show that the CIP 10-M yields slightly lower MDI monomer levels and higher MDI oligomer levels than those obtained with the bubblers. Mean negative bias for the MDI monomers was 14% (IC 95%: 2 - 26%) whereas positive bias for the MDI oligomers was 94% (IC 95%: 76 - 113%). The ASSET™ EZ4-NCO significantly underestimated MDI levels. The CIP 10-M seems to be a promising approach for testing exposure to MDI aerosols in the application of spray foam insulation.