A Cerement is one of the Whistimmu found in the Tempest in Wraith: The Oblivion. Cerements appear as large gobs of oozing ectoplasm with pulsating veins running throughout the substance. Cerements are one of the more benign types of Whistimmu, and will rarely go searching for trouble. However, if a wraith encounters one, they are in for a rough time; the unfortunate wraith that becomes entangled in a Cerement loses a year's worth of memories for every day they spend trapped within. Cerements can even pull their victim free of their Fetters and Passions, and use them as if they were its own. Eventually, the captured wraith will become a Cerement themselves.
The popular theory about the origin of Cerements holds that these Whistimmu were wraiths who failed to escape from their cauls before being pulled into the Tempest; there, the storm transforms into the so-called "flying body bags".