Enclosure
An enclosure is a closed housing around a 3D printer. It keeps the air around the print warm and free of draughts.
Why it matters
Materials that shrink a lot as they cool need a warm, steady environment. Prusa says ABS printers should sit inside an enclosure, and recommends one or a draft shield for ASA. Without one, these materials tend to warp.
Size matters too. Polymaker says small ABS models can print on an open printer with a 90 °C bed. Larger prints need an enclosed printer at roughly 40 to 50 °C, and very large ones a heated chamber.
Prusa also warns against creating a draft around the print. Fume removal still matters, so ventilate the room rather than blowing air across the part.
Some printers come fully enclosed, and others have add-on enclosures. A closed printer also holds the heat from the heated bed, which helps these materials.
If you only print easier materials, you may not need one. Check which materials you plan to use before paying for an enclosed printer.