Abstract: A waterbed mattress is disclosed having a cushioned box shaped frame with a base sheet securely attached to the box shaped frame, the combination forming therein cavity. A plurality of elongated fluid filled containers are disposed within the cavity, and two flat rectangularly shaped fluid filled envelopes are disposed over the elongated containers. The base sheet serves to hold the box shaped frame in substantially a rectangular shape. Additionally, the flat fluid filled envelopes provide a mattress with improved wave motion damping characteristics.