Baby bottles can have a single container, or two containers to create a space for thermal isolation, as selected by the user. The baby bottle can be vented to allow air to enter the bottle through a passageway as liquid is removed. A filter and one-way valve can be provided in the passageway. The passageway can be formed by radially aligning a vent opening in a top cap with a vent opening in a nipple flange, or by providing a channel in the top cap which is always in radial alignment with both the top cap vent opening and the flange vent opening.