There is no spoon
A sheet is a brush consisting of a single polygon – it has with zero width, will be invisible from an exact side-on viewpoint in the game. It can never block players, projectiles or other actors.
Sheet brushes can be added as any solidity: solid, semisolid, or nonsolid. The difference this makes is unclear, though some mappers swear by adding decorative sheets (eg draping CTF banners) as semisolids.
The surface of a sheet brush has all the normal surface properties of normal brushes: it can be made into a mirror, hold a texture, be made invisible, etc. Like any other surface, it's only visible from one side unless the Two Sided flag is set, either by using Add Special or setting Surface Flags (UT).
The red builder brush is shaped into a sheet by clicking the Sheet button: top right in the brushbuilders section of the toolbox, looks like a kind of kite shape stretched out horizontally. Right clicking on this gives you options of setting which way it is aligned (to X, to Y, or horizontally)
Common Uses of Sheets
- As invisible zone portals
- As water or lava zone portals (see Making Liquids (UT))
- Making Windows
- Used with masked textures to make grates, fences, etc
- Texture overlays, for example the rope lying around on the deck in UT's DM-KGalleon, or the ripple effect at the base of the waterfall in Unreal 1's Nyleve (see Making Waterfalls)
- To create draping banners, with team logos for example
- Flame effects: torches, fires, etc. The Volumetric brushbuilder produces a set of sheets specifically designed to do this (see Making Flames)
Do not use Intersection or DeIntersection on sheets!