A bottomless portafilter has had the spout and base removed this enables full view of the extraction as it passes through the filter basket. The quality of the extraction can be observed and the texture of the crema and then adjusted accordingly. It is also maintained by many fans of the naked portafilter that it allows the extraction to form better as there is less contact with metal.
Using a naked portafilter give you the opportunity to see the colouration, or 'Tiger Stripes', that appear when a good espresso is pulled through a bottomless portafilter.
The Rocket Espresso 58mm Bottomless Portafilter offers a clear view into the extraction process as rich hues of brown and caramel coffees are pulled through your portafilter only to waterfall into your shot glass like a thick molasses.