BABYLON.EdgesRenderer is a tool used to render edges on top of a mesh. Edges are rendered between two faces if the dot product of their normals is less than epsilon.

You can enable edges rendering like this:

var box = BABYLON.Mesh.CreateBox("box1", 2, scene);
box.enableEdgesRendering();    
box.edgesWidth = 4.0;
box.edgesColor = new BABYLON.Color4(0, 0, 1, 1);

The enableEdgesRendering can be called with a custom epsilon (default value is 0.95).

box.enableEdgesRendering(.9999);

Dot product is the cosine of the angle between the vectors, so for default epsilon 0.95 the angle is acos(.95) ~= 18 degrees - so if the angle between two faces is less than that no line gets drawn.

If you need to turn-off edges rendering:

box.disableEdgesRendering();

You can try edges rendering here: https://www.babylonjs-playground.com/#TYAHX#10 -