A teat for a feeding bottle has a one-way valve located remotely from the nipple of the teat to allow air to enter the feeding bottle to replace liquid sucked out of the bottle through the nipple while preventing liquid from leaking from the bottle. The one-way valve comprises an inwardly-oriented depression having opposed mutually inclined side walls meeting along a ridge having a slit. In the invention, when undeflected, the side walls make line contact with one another at the ridge and the thickness of the side walls is less than 0.4 mm so that, when acted upon by an increased pressure in the feeding bottle, the side walls collapse against one another and make sealing contact along a surface that extends from the ridge in the direction away from it.