An enclosure does two jobs. It holds heat around the print so materials like ABS, ASA and nylon do not warp or split, and it contains the fumes and fine particles printing releases so they can be filtered.
Temperature
A warm, draft-free chamber keeps layers from cooling unevenly. Doors and lids also keep dust, pets and curious hands away from hot parts.
Filtration
Activated carbon captures volatile organic compounds, the source of most printing odors. HEPA media captures ultrafine particles. Nevermore-style filters recirculate the chamber air through carbon, and many builds add a HEPA stage. Replace media on the manufacturer's schedule; saturated carbon stops working.
Room ventilation still matters
Filtration reduces exposure, but print rooms should still be ventilated, especially with several machines running.
