Onsite incinerators offer a promising solution to the challenges of menstrual waste disposal, particularly in institutional settings. However, thermochemical processes are well known to depend on the nature of the feedstocks and their moisture content (MC). An analysis is presented of the physical properties of menstrual waste as potential feedstock for onsite incinerators. Waste was generated in three institutional settings – from women of wide age range and from people with different socioeconomic backgrounds such as workers and students. Over 10 separate collections, 613 discarded menstrual pads were obtained with over 93% of the waste representing commercially disposable pads and less than 7% of the waste appearing to be homemade cloth pads. A surprising finding of this study was that a significant fraction of the commercially disposed pads (23–37%) had a large wet weight (over 20 g) which was associated with MC exceeding 50 wt%. This high MC was attributed to the practice of washing the pads prior to disposal, and it was much higher than what is standard for thermal processing. These data suggest that testing protocols for menstrual waste incinerator technology performance should include an evaluation of the effects of higher MC, unfolded pads, and occasional cloth pads.