While the kettle will still function without the anti-scale filter, the flow of the pour may not be as smooth and there may even be a little ‘spitting’ during the boil with a full kettle. And of course, the function of filtering out minerals from getting into the cup will not be there. We would always recommend using the anti-scale filter. While some are metal, many of our kettles use a plastic anti-scale filter – these are all BPA-free and food safe, and will not affect the water taste.