Abstract—A bench scale filtration apparatus was used to investigate the influence of powder composition, and tem-perature and humidity of the carrier gas on the structure of the filter cake formed in milk powder baghouses. Two types of powder, a skim milk powder (SMP) and a high fat milk protein concentrate (MPC) were filtered from air using a polyester filter, at a range of temperatures and humidity levels. The filter cake mass and pressure drop were meas-ured and used to calculate the cake permeability, and the filter cake structure was examined using a microscope. In-creased stickiness of particles resulted in the appearance of dendritic structures in the filter cake and hence an increase in porosity and reduction in cake resistance. Cake resistance in SMP was lowest at the highest relative humidity tested, indicating that cohesion in SMP was primarily due to the glass transition of amorphous lactose. The cake resistance in MPC was lowest at the highest temperatures tested, but was not affected by relative humidity, indicating that cohesion in this powder was primarily due to melted fat. In general, the MPC formed a more permeable filter cake and exhibited much higher deposition onto the filter than the SMP. The deposition rate of SMP powder decreased at higher relative humidity. The cause of this effect could not be determined, however likely explanations are increased agglomeration and gravitational settling of stickier powder prior to reach-ing the filter, or the breakage of fragile dendritic structures formed by sticky powder. The deposition rate of MPC was not affected by either temperature or humidity