diff --git a/lib/Slic3r/Extruder.pm b/lib/Slic3r/Extruder.pm
index fe20f50df..afacbd4f3 100644
--- a/lib/Slic3r/Extruder.pm
+++ b/lib/Slic3r/Extruder.pm
@@ -1,6 +1,7 @@
 package Slic3r::Extruder;
 use Moo;
 
+use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(scale unscale);
 
 has 'layer'              => (is => 'rw');
@@ -33,6 +34,16 @@ has 'speeds' => (
     }},
 );
 
+my %role_speeds = (
+    &EXTR_ROLE_PERIMETER       => 'perimeter',
+    &EXTR_ROLE_SMALLPERIMETER  => 'small_perimeter',
+    &EXTR_ROLE_FILL            => 'infill',
+    &EXTR_ROLE_SOLIDFILL       => 'solid_infill',
+    &EXTR_ROLE_BRIDGE          => 'bridge',
+    &EXTR_ROLE_SKIRT           => 'perimeter',
+    &EXTR_ROLE_SUPPORTMATERIAL => 'perimeter',
+);
+
 use Slic3r::Geometry qw(points_coincide PI X Y);
 
 sub change_layer {
@@ -126,7 +137,7 @@ sub extrude_path {
     my $w = ($s - $Slic3r::min_flow_spacing * $Slic3r::overlap_factor) / (1 - $Slic3r::overlap_factor);
     
     my $area;
-    if ($path->role eq 'bridge') {
+    if ($path->role == EXTR_ROLE_BRIDGE) {
         $area = ($s**2) * PI/4;
     } elsif ($w >= ($Slic3r::nozzle_diameter + $h)) {
         # rectangle with semicircles at the ends
@@ -142,14 +153,7 @@ sub extrude_path {
         * (4 / (($Slic3r::filament_diameter ** 2) * PI));
     
     # extrude arc or line
-    $self->speed(
-        $path->role =~ /^(perimeter|skirt|support-material)$/o ? 'perimeter'
-            : $path->role eq 'small-perimeter'  ? 'small_perimeter'
-            : $path->role eq 'fill'             ? 'infill'
-            : $path->role eq 'solid-fill'       ? 'solid_infill'
-            : $path->role eq 'bridge'           ? 'bridge'
-            : die "Unknown role: " . $path->role
-    );
+    $self->speed( $role_speeds{$path->role} || die "Unknown role: " . $path->role );
     my $path_length = 0;
     if ($path->isa('Slic3r::ExtrusionPath::Arc')) {
         $path_length = $path->length;
diff --git a/lib/Slic3r/ExtrusionLoop.pm b/lib/Slic3r/ExtrusionLoop.pm
index 1c4c327bb..5f00906cc 100644
--- a/lib/Slic3r/ExtrusionLoop.pm
+++ b/lib/Slic3r/ExtrusionLoop.pm
@@ -1,7 +1,6 @@
 package Slic3r::ExtrusionLoop;
 use Moo;
 
-
 # the underlying Slic3r::Polygon objects holds the geometry
 has 'polygon' => (
     is          => 'ro',
@@ -9,7 +8,7 @@ has 'polygon' => (
     handles     => [qw(is_printable nearest_point_to)],
 );
 
-# perimeter/fill/solid-fill/bridge/skirt
+# see EXTR_ROLE_* constants in ExtrusionPath.pm
 has 'role'         => (is => 'rw', required => 1);
 
 sub BUILD {
diff --git a/lib/Slic3r/ExtrusionPath.pm b/lib/Slic3r/ExtrusionPath.pm
index 6927cc0b0..67bdf3577 100644
--- a/lib/Slic3r/ExtrusionPath.pm
+++ b/lib/Slic3r/ExtrusionPath.pm
@@ -1,6 +1,13 @@
 package Slic3r::ExtrusionPath;
 use Moo;
 
+require Exporter;
+our @ISA = qw(Exporter);
+our @EXPORT_OK = qw(EXTR_ROLE_PERIMETER EXTR_ROLE_SMALLPERIMETER EXTR_ROLE_FILL EXTR_ROLE_SOLIDFILL
+    EXTR_ROLE_BRIDGE EXTR_ROLE_SKIRT EXTR_ROLE_SUPPORTMATERIAL);
+our %EXPORT_TAGS = (roles => \@EXPORT_OK);
+
+
 use Slic3r::Geometry qw(PI X Y epsilon deg2rad rotate_points);
 
 # the underlying Slic3r::Polyline objects holds the geometry
@@ -16,8 +23,14 @@ has 'depth_layers' => (is => 'ro', default => sub {1});
 
 has 'flow_spacing' => (is => 'rw');
 
-# perimeter/fill/solid-fill/bridge/skirt/support-material
 has 'role'         => (is => 'rw', required => 1);
+use constant EXTR_ROLE_PERIMETER        => 0;
+use constant EXTR_ROLE_SMALLPERIMETER   => 1;
+use constant EXTR_ROLE_FILL             => 2;
+use constant EXTR_ROLE_SOLIDFILL        => 3;
+use constant EXTR_ROLE_BRIDGE           => 4;
+use constant EXTR_ROLE_SKIRT            => 5;
+use constant EXTR_ROLE_SUPPORTMATERIAL  => 6;
 
 sub BUILD {
     my $self = shift;
diff --git a/lib/Slic3r/Fill.pm b/lib/Slic3r/Fill.pm
index 1842d4f6d..6a892277b 100644
--- a/lib/Slic3r/Fill.pm
+++ b/lib/Slic3r/Fill.pm
@@ -11,6 +11,7 @@ use Slic3r::Fill::Line;
 use Slic3r::Fill::OctagramSpiral;
 use Slic3r::Fill::PlanePath;
 use Slic3r::Fill::Rectilinear;
+use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(X Y scale shortest_path);
 use Slic3r::Geometry::Clipper qw(union_ex diff_ex);
 
@@ -165,7 +166,9 @@ sub make_fill {
             paths => [
                 map Slic3r::ExtrusionPath->new(
                     polyline => Slic3r::Polyline->new(@$_),
-                    role => ($is_bridge ? 'bridge' : $is_solid ? 'solid-fill' : 'fill'),
+                    role => ($is_bridge ? EXTR_ROLE_BRIDGE
+                        : $is_solid ? EXTR_ROLE_SOLIDFILL
+                        : EXTR_ROLE_FILL),
                     depth_layers => $surface->depth_layers,
                     flow_spacing => $params->{flow_spacing},
                 ), @paths,
@@ -178,8 +181,8 @@ sub make_fill {
         paths => [
             map {
                 $_->isa('Slic3r::Polygon')
-                    ? Slic3r::ExtrusionLoop->new(polygon => $_, role => 'solid-fill')->split_at($_->[0])
-                    : Slic3r::ExtrusionPath->new(polyline => $_, role => 'solid-fill')
+                    ? Slic3r::ExtrusionLoop->new(polygon => $_, role => EXTR_ROLE_SOLIDFILL)->split_at($_->[0])
+                    : Slic3r::ExtrusionPath->new(polyline => $_, role => EXTR_ROLE_SOLIDFILL)
             } @{$layer->thin_fills},
         ],
     ) if @{$layer->thin_fills};
diff --git a/lib/Slic3r/Fill/Concentric.pm b/lib/Slic3r/Fill/Concentric.pm
index 5c97490d0..b3d4fbedf 100644
--- a/lib/Slic3r/Fill/Concentric.pm
+++ b/lib/Slic3r/Fill/Concentric.pm
@@ -3,6 +3,7 @@ use Moo;
 
 extends 'Slic3r::Fill::Base';
 
+use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(scale unscale X1 Y1 X2 Y2);
 
 sub fill_surface {
@@ -50,7 +51,7 @@ sub fill_surface {
         ($bounding_box->[X1] + $bounding_box->[X2]) / 2,
         ($bounding_box->[Y1] + $bounding_box->[Y2]) / 2,
     );
-    foreach my $loop (map Slic3r::ExtrusionLoop->new(polygon => $_, role => 'fill'), @loops) {
+    foreach my $loop (map Slic3r::ExtrusionLoop->new(polygon => $_, role => EXTR_ROLE_FILL), @loops) {
         # extrude all loops ccw
         $loop->polygon->make_counter_clockwise;
         
diff --git a/lib/Slic3r/Fill/Rectilinear.pm b/lib/Slic3r/Fill/Rectilinear.pm
index af1508c52..ad6a82e45 100644
--- a/lib/Slic3r/Fill/Rectilinear.pm
+++ b/lib/Slic3r/Fill/Rectilinear.pm
@@ -57,7 +57,7 @@ sub fill_surface {
     # connect lines
     {
         my $collection = Slic3r::ExtrusionPath::Collection->new(
-            paths => [ map Slic3r::ExtrusionPath->new(polyline => Slic3r::Polyline->new(@$_), role => 'bogus'), @paths ],
+            paths => [ map Slic3r::ExtrusionPath->new(polyline => Slic3r::Polyline->new(@$_), role => -1), @paths ],
         );
         @paths = ();
         
diff --git a/lib/Slic3r/Layer.pm b/lib/Slic3r/Layer.pm
index 6002b5e73..2e0b48ec8 100644
--- a/lib/Slic3r/Layer.pm
+++ b/lib/Slic3r/Layer.pm
@@ -2,6 +2,7 @@ package Slic3r::Layer;
 use Moo;
 
 use Math::Clipper ':all';
+use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(scale unscale collinear X Y A B PI rad2deg_dir bounding_box_center shortest_path);
 use Slic3r::Geometry::Clipper qw(union_ex diff_ex intersection_ex xor_ex is_counter_clockwise);
 
@@ -283,26 +284,26 @@ sub make_perimeters {
         }
         
         foreach my $hole (reverse @holes) {
-            push @{ $self->perimeters }, Slic3r::ExtrusionLoop->new(polygon => $hole, role => 'perimeter');
+            push @{ $self->perimeters }, Slic3r::ExtrusionLoop->new(polygon => $hole, role => EXTR_ROLE_PERIMETER);
         }
         
         # do contours starting from innermost one
         foreach my $contour (map $_->contour, map @$_, reverse @$island) {
-            push @{ $self->perimeters }, Slic3r::ExtrusionLoop->new(polygon => $contour, role => 'perimeter');
+            push @{ $self->perimeters }, Slic3r::ExtrusionLoop->new(polygon => $contour, role => EXTR_ROLE_PERIMETER);
         }
     }
     
     # detect small perimeters by checking their area
     for (@{ $self->perimeters }) {
-        $_->role('small-perimeter') if abs($_->polygon->length) <= $Slic3r::small_perimeter_length;
+        $_->role(EXTR_ROLE_SMALLPERIMETER) if abs($_->polygon->length) <= $Slic3r::small_perimeter_length;
     }
     
     # add thin walls as perimeters
     for (@{ $self->thin_walls }) {
         if ($_->isa('Slic3r::Polygon')) {
-            push @{ $self->perimeters }, Slic3r::ExtrusionLoop->new(polygon => $_, role => 'perimeter');
+            push @{ $self->perimeters }, Slic3r::ExtrusionLoop->new(polygon => $_, role => EXTR_ROLE_PERIMETER);
         } else {
-            push @{ $self->perimeters }, Slic3r::ExtrusionPath->new(polyline => $_, role => 'perimeter');
+            push @{ $self->perimeters }, Slic3r::ExtrusionPath->new(polyline => $_, role => EXTR_ROLE_PERIMETER);
         }
     }
 }
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index 2a1aad22f..c064ee68b 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -3,6 +3,7 @@ use Moo;
 
 use File::Basename qw(basename fileparse);
 use Math::ConvexHull 1.0.4 qw(convex_hull);
+use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(X Y Z X1 Y1 X2 Y2 PI scale unscale move_points);
 use Slic3r::Geometry::Clipper qw(diff_ex union_ex offset JT_ROUND);
 use Time::HiRes qw(gettimeofday tv_interval);
@@ -369,7 +370,7 @@ sub make_skirt {
         my $outline = offset([$convex_hull], $distance, $Slic3r::scaling_factor * 100, JT_ROUND);
         push @skirt, Slic3r::ExtrusionLoop->new(
             polygon => Slic3r::Polygon->new(@{$outline->[0]}),
-            role => 'skirt',
+            role => EXTR_ROLE_SKIRT,
         );
     }
     push @{$self->skirt}, @skirt;
diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 5e403f8fd..60d91143a 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -1,6 +1,7 @@
 package Slic3r::Print::Object;
 use Moo;
 
+use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(scale unscale);
 use Slic3r::Geometry::Clipper qw(diff_ex intersection_ex union_ex);
 
@@ -542,7 +543,7 @@ sub generate_support_material {
                 push @patterns,
                     map Slic3r::ExtrusionPath->new(
                         polyline        => Slic3r::Polyline->new(@$_),
-                        role            => 'support-material',
+                        role            => EXTR_ROLE_SUPPORTMATERIAL,
                         depth_layers    => 1,
                         flow_spacing    => $params->{flow_spacing},
                     ), @paths;
diff --git a/t/arcs.t b/t/arcs.t
index 2589e908f..b63c2660e 100644
--- a/t/arcs.t
+++ b/t/arcs.t
@@ -10,6 +10,7 @@ BEGIN {
 }
 
 use Slic3r;
+use Slic3r::ExtrusionPath ':roles';
 use Slic3r::Geometry qw(epsilon);
 
 {
@@ -19,7 +20,7 @@ use Slic3r::Geometry qw(epsilon);
         [306517.1,219034.23], [286979.42,248012.49], [258001.16,267550.17], [222515.14,274714.47], 
         [187029.11,267550.17], [158050.85,248012.49], [138513.17,219034.23], [131348.87,183548.2], 
         [86948.77,175149.09], [119825.35,100585],
-    ), role => 'fill');
+    ), role => EXTR_ROLE_FILL);
     
     my $collection = Slic3r::ExtrusionPath::Collection->new(paths => [$path]);
     $collection->detect_arcs(30);
@@ -37,10 +38,10 @@ use Slic3r::Geometry qw(epsilon);
         [13.8268343236509,19.2387953251129], [14.5399049973955,18.9100652418837], 
         [15.2249856471595,18.5264016435409], [15.8778525229247,18.0901699437495], 
         [16.4944804833018,17.6040596560003],
-    ), role => 'fill');
+    ), role => EXTR_ROLE_FILL);
     my $path2 = Slic3r::ExtrusionPath->new(
         polyline    => Slic3r::Polyline->new(reverse @{$path1->points}),
-        role        => 'fill',
+        role        => EXTR_ROLE_FILL,
     );
     
     my $collection1 = Slic3r::ExtrusionPath::Collection->new(paths => [$path1]);