Freemie SlimFit Cups were made for use with Freemie rechargeable pumps, including Independence II, Liberty II and Rose. These cups are closed-system and have a barrier inside to prevent milk from backing up.

SlimFit5 and SlimFit6 Cups can be used with a new Spectra S1 Plus, S2 Plus, or 9+ Pump. 

Use of Freemie Cups with an unapproved pump or "hack" is never recommended and may cause damage, malfunction, or injury.