I used the cap the first week of my evolve use, then I put a glass globe with a 6" whip in place of the atty tip. I observed in real time the vapor patterns rising out of the evolve + atty & determined that it hardly mattered at all cap on/cap off , actually restricted flow slightly and was a waste of time & effort and made more of a mess. With the Clear glass bowl covering the atty, you see & feel all kinds of things I never knew or understood, very cool looking & vapor also cooler. I have used not only the Evolve, but the Yocan Cerum & Nyx also fit well. The air flow is better on both, and the Cerum is all ceramic.