Why is glass material increasing noise, and what to do about it? I have a quite simple rendering in Cycles, containing some droplets with a standard glass material – only glass node, connected to surface of material node.

The problem is, the glass increases the noise enormously. First Picture with glass:



Second picture for comparison with plain white diffuse material instead of glass:



This is just an extremly simple scene, and it's just rendered with 32 samples for testing purposes.

Is there a way to reduce the noise added by glass material? Please keep in mind, this is not about the noise in glass itself, but about added noise everywhere else.
Short version: glass shader is more complicated and needs more calculations to obtain a nice result. So either you set samples to higher values, either you use some trickeries in the shader or in the rendering settings in order to reduce the complexity (but at the cost of accuracy).

I invite you to read the Blender Manual about Glass BSDF, which explains this more precisely as well as giving you ways to reduce noise.