6 Things that increase the Render time

Volumetric Lighting

With Volumetrics, we can show light rays and we can even create fog. But Volumetric lighting increases render time.

High Poly Mesh

Some times, the mesh has unnecessarily high poly count which can affect the Render time.

Environment Textures

Environment textures, sometimes referred as HDRI, are very effective for beautiful lighting. But they can cost you render time.

Fluids

Fluids can enhance the scene, but it can take longer for the scenes to render.

High Quality Textures

For high quality models, we use High Quality texture maps. But they can cost us increased render time.

Hair

Hair can be very useful in making realistic scenes, but they take longer time to render.

Other causes

Using Cycles instead of Eevee. Having High Samples for Rendering. Low End PC. Using CPU instead of GPU for rendering.