Ulmus Rubra Herbal Supplement Non-Irradiated Kosher This product is the powdered inner bark of the slippery elm tree. The quality of true slippery elm bark powder can be determined fairly easily by dissolving a sample in boiling water. The sample should produce a light brown to pinkish brown tea with a slippery feel between the fingers. Upon cooling the mixture coagulates slightly. Slippery Elm is a small tree native to North America. The bark is harvested from the tree in the early spring and the outer bark is scraped off, leaving the mucilage-rich inner bark. Nature's gentle demulcent.