After some searching, I found another solution to properly render only the wireframe of the triangles, here it is:.... func render(renderCommandEncoder: MTLRenderCommandEncoder){ renderCommandEncoder.setTriangleFillMode(.lines) renderCommandEncoder.setRenderPipelineState(RenderPipelineStateLibrary.PipelineState(.Basic)) renderCommandEncoder.setVertexBuffer(mesh.vertexBuffer, offset: 0, index: 0) renderCommandEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: mesh.vertexCount) }