Blend Mode
How a material combines with what is behind it
Also known as: Material blend mode · Opaque vs Masked vs Translucent · Opacity mask · Masked material · Translucent material
Definition
A material's Blend Mode in Unreal Engine decides how its output is combined with the pixels already drawn behind it. The common modes are Opaque, Masked, which cuts pixels fully on or off using an Opacity Mask, and Translucent, which blends smoothly by opacity. Epic's documentation also lists Additive, Modulate, Alpha Composite and Alpha Holdout. Opaque is the default and the cheapest, so choosing another mode is a trade of quality against cost.
In production
Use Opaque for almost everything. Use Masked for leaves, fences and hair cards, where each pixel is either there or not, and Translucent for glass, smoke and water, where partial transparency is needed. Translucent surfaces are sorted, do not write depth the way opaque ones do, and overlap so that pixels are shaded several times, which makes them expensive. If a translucent material costs too much, check whether Masked or a dithered opacity could do the job.
Tools that use Blend Mode
See also
Overdraw
Redrawing same pixels
Shader Complexity
Viewport view of per-pixel material cost
Master Material
Parent material that spawns instances
Decal
Projected texture detail on existing surfaces
Subsurface Scattering
Light entering and bouncing inside a material
Additive vs Alpha Blending
Two ways particles combine with the scene
Particles Render in the Wrong Order
Effects pop in front or behind each other
Depth Fade (Soft Particles)
Fades a surface where it meets other geometry