diff --git a/oscope-sphere/bin/data/shaders/sphere.frag b/oscope-sphere/bin/data/shaders/sphere.frag
index fb73cc3..e22ab9d 100644
--- a/oscope-sphere/bin/data/shaders/sphere.frag
+++ b/oscope-sphere/bin/data/shaders/sphere.frag
@@ -46,6 +46,12 @@ void main() {
         return;
     }
 
+    if (renderMode == 2) {
+        // wireframe: bright unlit colormap lines
+        fragColor = vec4(col * 1.4 + vec3(0.06), 1.0);
+        return;
+    }
+
     // skin: light the displaced relief with a screen-space face normal
     vec3 N = normalize(cross(dFdx(vViewPos), dFdy(vViewPos)));
     vec3 V = normalize(-vViewPos);
diff --git a/oscope-sphere/bin/data/shaders/sphere.vert b/oscope-sphere/bin/data/shaders/sphere.vert
index 140fa99..caac742 100644
--- a/oscope-sphere/bin/data/shaders/sphere.vert
+++ b/oscope-sphere/bin/data/shaders/sphere.vert
@@ -34,6 +34,8 @@ void main() {
     if (renderMode == 1) {
         r *= 1.06;                  // float the point cloud outside the skin
         gl_PointSize = 6.0;
+    } else if (renderMode == 2) {
+        r *= 1.01;                  // wireframe sits just above the lit skin
     }
 
     vec4 viewPos = modelViewMatrix * vec4(dir * r, 1.0);
diff --git a/oscope-sphere/src/SphereViz.cpp b/oscope-sphere/src/SphereViz.cpp
index cc25d4d..cba09d6 100644
--- a/oscope-sphere/src/SphereViz.cpp
+++ b/oscope-sphere/src/SphereViz.cpp
@@ -98,3 +98,11 @@ void SphereViz::drawPoints() {
     pointsMesh_.draw();
     shader_.end();
 }
+
+void SphereViz::drawWireframe() {
+    shader_.begin();
+    bindUniforms();
+    shader_.setUniform1i("renderMode", 2);
+    mesh_.drawWireframe();
+    shader_.end();
+}
diff --git a/oscope-sphere/src/SphereViz.h b/oscope-sphere/src/SphereViz.h
index 316f488..a0c6e69 100644
--- a/oscope-sphere/src/SphereViz.h
+++ b/oscope-sphere/src/SphereViz.h
@@ -19,6 +19,7 @@ public:
 
     void drawSkin();
     void drawPoints();
+    void drawWireframe();
     void setColormap(int id) { colormapId_ = id; }
 
 private:
diff --git a/oscope-sphere/src/ofApp.cpp b/oscope-sphere/src/ofApp.cpp
index e591423..119a695 100644
--- a/oscope-sphere/src/ofApp.cpp
+++ b/oscope-sphere/src/ofApp.cpp
@@ -72,6 +72,7 @@ void ofApp::draw() {
     ofRotateXDeg(16.0f * std::sin(t * 0.27f));   // slow tumble
     ofScale(pulse_, pulse_, pulse_);             // audio pulse
     if (layerA_) sphere_.drawSkin();
+    if (layerD_) sphere_.drawWireframe();
     if (layerC_) sphere_.drawPoints();
     if (layerB_) rings_.draw();
     ofPopMatrix();
@@ -86,6 +87,7 @@ void ofApp::drawHud() {
     hud += std::string("[1] skin   ") + (layerA_ ? "on" : "off") + "\n";
     hud += std::string("[2] rings  ") + (layerB_ ? "on" : "off") + "\n";
     hud += std::string("[3] points ") + (layerC_ ? "on" : "off") + "\n";
+    hud += std::string("[4] wire   ") + (layerD_ ? "on" : "off") + "\n";
     hud += std::string("[c] colormap   [space] ") +
            (frozen_ ? "frozen" : "live");
     ofDrawBitmapString(hud, 16, 24);
@@ -97,6 +99,7 @@ void ofApp::keyPressed(int key) {
         case '1': layerA_ = !layerA_; break;
         case '2': layerB_ = !layerB_; break;
         case '3': layerC_ = !layerC_; break;
+        case '4': layerD_ = !layerD_; break;
         case 'c':
         case 'C': colormap_ = (colormap_ + 1) % 2; break;
         case ' ': frozen_ = !frozen_; break;
diff --git a/oscope-sphere/src/ofApp.h b/oscope-sphere/src/ofApp.h
index e2d5c6d..c74a06d 100644
--- a/oscope-sphere/src/ofApp.h
+++ b/oscope-sphere/src/ofApp.h
@@ -35,6 +35,7 @@ private:
     bool  layerA_   = true;
     bool  layerB_   = true;
     bool  layerC_   = true;
+    bool  layerD_   = true;
     int   colormap_ = 0;
     float scopeSr_  = 16.0e6f;
     float spin_     = 0.0f;