For certain bottles brands an adapter is needed in order to fit the warmer onto the bottle. When ordering you can choose your own bottle brand and make sure you get the right fit. If your bottle is not on the bottle brand list, then simply select 'Other Brand' before adding it to your cart.Compatible with the following bottle brands: AVENTTommee TippeeHegen (square bottle)MAMPigeon (all sizes)HaakaaNUK (all sizes)Dr. Brown's (all sizes)MedelaNanobebe (all sizes)NubyDodieSuavinexAnd many more!If you have any questions about which bottle brand to choose from or multi-brand compatibility, please ask us in chat or by email!