Glass is a clear, ink-resistant surface; ink that hits it instantly dissolves away. Since Inklings and Octolings cannot swim over it, it is more efficient to run across in humanoid form. Glass is also slightly transparent, so the player can look at what is under it.
Glass can be found on the walls and floors of several stages — Urchin Underpass has both platforms and walls made of glass in its side alleys. It sees a minor use in some other stages, including Arowana Mall, Camp Triggerfish, and Port Mackerel.
Glass also appears during the final stage of The Rampaging Octowhirl!, the third boss battle in Octo Valley. Some of the rotating floor is destroyed, making it harder for Agent 3 to get the Octowhirl caught in their ink. It is also used in some other missions, such as Propeller Lift Fortress.
Glass appears in the returning stages from Splatoon, while making new appearances. It functions the same as in the previous game. Shellendorf Institute prominently features glass, as there is a raised glass roof on top of the central area. Goby Arena also has some glass at the start of the lower area of the stage. Wahoo World has glass walkways near the center carousel which is also contained in glass.
There are also multiple Shifty Stations that use glass:
- The Bunker Games: The dome and cubes that lowers onto the stage are made of glass.
- Zappy Longshocking: Glass is used to separate teams at the start of a match.
- Sweet Valley Tentacles: The walls that sink into the ground after popping a tentacle are made of glass.
- Bridge to Tentaswitchia: The dome surrounding the Ink Switch that moves the floor and the wall that prevents the player from inking the floor that has passed is made of glass.
In addition to returning stages from Splatoon and Splatoon 2, Undertow Spillway features glass walkways overlooking its central area, as well as supporting columns covered in glass. Scorch Gorge's Tricolor Turf War layout also features glass. It has glass triangles in the middle, as well as a line of glass in the defenders spawn. On every side are also glass pillars.
- Glass can be seen with stickers on it in Urchin Underpass. If the stickers get looked at too closely, they become low resolution.
- The train in Inkopolis Plaza is an example of a place where the glass is not transparent.
- In Inkopolis Plaza, the player can see reflections from glass with a black filter by Spyke. Any of the windows that have a sticker with an arrow pointing down with a squid shape is one of these when in the lobby.
Some glass in the old version of Urchin Underpass.