diff --git a/lib/Slic3r/Format/STL.pm b/lib/Slic3r/Format/STL.pm
index 2d537c126..ed7984f4c 100644
--- a/lib/Slic3r/Format/STL.pm
+++ b/lib/Slic3r/Format/STL.pm
@@ -1,20 +1,17 @@
 package Slic3r::Format::STL;
 use Moo;
 
-use Slic3r::Geometry qw(X Y Z triangle_normal);
-
 sub read_file {
     my $self = shift;
     my ($file) = @_;
     
-    my $tmesh = Slic3r::TriangleMesh->new;
-    $tmesh->ReadSTLFile(Slic3r::encode_path($file));
-    $tmesh->repair;
-    my ($vertices, $facets) = ($tmesh->vertices, $tmesh->facets);
+    my $mesh = Slic3r::TriangleMesh->new;
+    $mesh->ReadSTLFile(Slic3r::encode_path($file));
+    $mesh->repair;
     
     my $model = Slic3r::Model->new;
-    my $object = $model->add_object(vertices => $vertices, mesh_stats => $tmesh->stats);
-    my $volume = $object->add_volume(facets => $facets);
+    my $object = $model->add_object;
+    my $volume = $object->add_volume(mesh => $mesh);
     return $model;
 }
 
@@ -22,48 +19,11 @@ sub write_file {
     my $self = shift;
     my ($file, $model, %params) = @_;
     
-    Slic3r::open(\my $fh, '>', $file);
+    my $path = Slic3r::encode_path($file);
     
     $params{binary}
-        ? _write_binary($fh, $model->mesh)
-        : _write_ascii($fh, $model->mesh);
-    
-    close $fh;
-}
-
-sub _write_binary {
-    my ($fh, $mesh) = @_;
-    
-    die "bigfloat" unless length(pack "f", 1) == 4;
-    
-    binmode $fh;
-    print $fh pack 'x80';
-    print $fh pack 'L', scalar(@{$mesh->facets});
-    foreach my $facet (@{$mesh->facets}) {
-        print $fh pack '(f<3)4S',
-            @{_facet_normal($mesh, $facet)},
-            (map @{$mesh->vertices->[$_]}, @$facet[-3..-1]),
-            0;
-    }
-}
-
-sub _write_ascii {
-    my ($fh, $mesh) = @_;
-    
-    printf $fh "solid\n";
-    foreach my $facet (@{$mesh->facets}) {
-        printf $fh "   facet normal %f %f %f\n", @{_facet_normal($mesh, $facet)};
-        printf $fh "      outer loop\n";
-        printf $fh "         vertex %f %f %f\n", @{$mesh->vertices->[$_]} for @$facet[-3..-1];
-        printf $fh "      endloop\n";
-        printf $fh "   endfacet\n";
-    }
-    printf $fh "endsolid\n";
-}
-
-sub _facet_normal {
-    my ($mesh, $facet) = @_;
-    return triangle_normal(map $mesh->vertices->[$_], @$facet[-3..-1]);
+        ? $model->mesh->write_binary($path)
+        : $model->mesh->write_ascii($path);
 }
 
 1;
diff --git a/lib/Slic3r/Model.pm b/lib/Slic3r/Model.pm
index 9667e6db2..2052df8b1 100644
--- a/lib/Slic3r/Model.pm
+++ b/lib/Slic3r/Model.pm
@@ -315,32 +315,21 @@ use Storable qw(dclone);
 
 has 'input_file' => (is => 'rw');
 has 'model'     => (is => 'ro', weak_ref => 1, required => 1);
-has 'vertices'  => (is => 'ro', default => sub { [] });
 has 'volumes'   => (is => 'ro', default => sub { [] });
 has 'instances' => (is => 'rw');
 has 'config'    => (is => 'rw', default => sub { Slic3r::Config->new });
 has 'layer_height_ranges' => (is => 'rw', default => sub { [] }); # [ z_min, z_max, layer_height ]
 has 'material_mapping'      => (is => 'rw', default => sub { {} }); # { material_id => extruder_idx }
-has 'mesh_stats' => (is => 'rw');
 has '_bounding_box' => (is => 'rw');
 
 sub add_volume {
     my $self = shift;
     my %args = @_;
     
-    if (my $vertices = delete $args{vertices}) {
-        my $v_offset = @{$self->vertices};
-        push @{$self->vertices}, @$vertices;
-        
-        @{$args{facets}} = map {
-            my $f = [@$_];
-            $f->[$_] += $v_offset for -3..-1;
-            $f;
-        } @{$args{facets}};
-    }
-    
-    my $volume = Slic3r::Model::Volume->new(object => $self, %args);
-    push @{$self->volumes}, $volume;
+    push @{$self->volumes}, my $volume = Slic3r::Model::Volume->new(
+        object => $self,
+        %args,
+    );
     $self->_bounding_box(undef);
     $self->model->_bounding_box(undef);
     return $volume;
@@ -358,16 +347,14 @@ sub add_instance {
 sub mesh {
     my $self = shift;
     
-    # this mesh won't be suitable for check_manifoldness as multiple
-    # facets from different volumes may use the same vertices
     my $mesh = Slic3r::TriangleMesh->new;
-    $mesh->ReadFromPerl($self->vertices, [ map @{$_->facets}, @{$self->volumes} ]);
+    $mesh->merge($_->mesh) for @{$self->volumes};
     return $mesh;
 }
 
 sub used_vertices {
     my $self = shift;
-    return [ map $self->vertices->[$_], map @$_, map @{$_->facets}, @{$self->volumes} ];
+    return [ map $_->mesh->used_vertices, @{$self->volumes} ];
 }
 
 sub size {
@@ -389,7 +376,8 @@ sub bounding_box {
     my $self = shift;
     
     if (!defined $self->_bounding_box) {
-        $self->_bounding_box(Slic3r::Geometry::BoundingBox->new_from_points_3D($self->used_vertices));
+        # TODO: calculate bb in XS
+        $self->_bounding_box(Slic3r::Geometry::BoundingBox->new_from_points_3D(map $_->mesh->vertices, @{$self->volumes}));
     }
     return $self->_bounding_box;
 }
@@ -409,7 +397,7 @@ sub move {
     my $self = shift;
     my @shift = @_;
     
-    @{$self->vertices} = move_points_3D([ @shift ], @{$self->vertices});
+    $_->mesh->translate(@shift) for @{$self->volumes};
     $self->_bounding_box->translate(@shift) if defined $self->_bounding_box;
 }
 
@@ -418,13 +406,8 @@ sub scale {
     my ($factor) = @_;
     return if $factor == 1;
     
-    # transform vertex coordinates
-    foreach my $vertex (@{$self->vertices}) {
-        $vertex->[$_] *= $factor for X,Y,Z;
-    }
-    
+    $_->mesh->scale($factor) for @{$self->volumes};
     $self->_bounding_box->scale($factor) if defined $self->_bounding_box;
-    $self->mesh_stats->{volume} *= ($factor**3) if defined $self->mesh_stats;
 }
 
 sub rotate {
@@ -432,13 +415,7 @@ sub rotate {
     my ($deg) = @_;
     return if $deg == 0;
     
-    my $rad = Slic3r::Geometry::deg2rad($deg);
-    
-    # transform vertex coordinates
-    foreach my $vertex (@{$self->vertices}) {
-        @$vertex = (@{ +(Slic3r::Geometry::rotate_points($rad, undef, [ $vertex->[X], $vertex->[Y] ]))[0] }, $vertex->[Z]);
-    }
-    
+    $_->mesh->rotate($deg, Slic3r::Point->(0,0)) for @{$self->volumes};
     $self->_bounding_box(undef);
 }
 
@@ -499,20 +476,7 @@ use Moo;
 
 has 'object'        => (is => 'ro', weak_ref => 1, required => 1);
 has 'material_id'   => (is => 'rw');
-has 'facets'        => (is => 'rw', default => sub { [] });
-
-sub mesh {
-    my $self = shift;
-    
-    my $mesh = Slic3r::TriangleMesh->new;
-    $mesh->ReadFromPerl($self->object->vertices, $self->facets);
-    return $mesh;
-}
-
-sub facets_count {
-    my $self = shift;
-    return scalar(@{$self->facets});  # TODO: optimize in XS
-}
+has 'mesh'          => (is => 'rw', required => 1);
 
 package Slic3r::Model::Instance;
 use Moo;
diff --git a/lib/Slic3r/TriangleMesh.pm b/lib/Slic3r/TriangleMesh.pm
index 7831e5057..434b5ada2 100644
--- a/lib/Slic3r/TriangleMesh.pm
+++ b/lib/Slic3r/TriangleMesh.pm
@@ -24,6 +24,11 @@ sub used_vertices {
     return $self->vertices;
 }
 
+sub facets_count {
+    my $self = shift;
+    return $self->stats->{number_of_facets};
+}
+
 sub bounding_box {
     my $self = shift;
     return Slic3r::Geometry::BoundingBox->new_from_points_3D($self->used_vertices);
diff --git a/xs/src/TriangleMesh.cpp b/xs/src/TriangleMesh.cpp
index 8f6ac0b10..81cebb7d8 100644
--- a/xs/src/TriangleMesh.cpp
+++ b/xs/src/TriangleMesh.cpp
@@ -50,6 +50,18 @@ TriangleMesh::ReadSTLFile(char* input_file) {
     stl_open(&stl, input_file);
 }
 
+void
+TriangleMesh::write_ascii(char* output_file)
+{
+    stl_write_ascii(&this->stl, output_file, "");
+}
+
+void
+TriangleMesh::write_binary(char* output_file)
+{
+    stl_write_binary(&this->stl, output_file, "");
+}
+
 void TriangleMesh::ReadFromPerl(SV* vertices, SV* facets)
 {
     stl_initialize(&stl);
diff --git a/xs/src/TriangleMesh.hpp b/xs/src/TriangleMesh.hpp
index b47f368ed..30729bf63 100644
--- a/xs/src/TriangleMesh.hpp
+++ b/xs/src/TriangleMesh.hpp
@@ -20,6 +20,8 @@ class TriangleMesh
     ~TriangleMesh();
     SV* to_SV();
     void ReadSTLFile(char* input_file);
+    void write_ascii(char* output_file);
+    void write_binary(char* output_file);
     void ReadFromPerl(SV* vertices, SV* facets);
     void repair();
     void WriteOBJFile(char* output_file);
diff --git a/xs/src/admesh/stl.h b/xs/src/admesh/stl.h
index 04aa8220d..699044866 100644
--- a/xs/src/admesh/stl.h
+++ b/xs/src/admesh/stl.h
@@ -139,8 +139,8 @@ extern void stl_close(stl_file *stl);
 extern void stl_stats_out(stl_file *stl, FILE *file, char *input_file);
 extern void stl_print_edges(stl_file *stl, FILE *file);
 extern void stl_print_neighbors(stl_file *stl, char *file);
-extern void stl_write_ascii(stl_file *stl, char *file, char *label);
-extern void stl_write_binary(stl_file *stl, char *file, char *label);
+extern void stl_write_ascii(stl_file *stl, const char *file, const char *label);
+extern void stl_write_binary(stl_file *stl, const char *file, const char *label);
 extern void stl_check_facets_exact(stl_file *stl);
 extern void stl_check_facets_nearby(stl_file *stl, float tolerance);
 extern void stl_remove_unconnected_facets(stl_file *stl);
diff --git a/xs/src/admesh/stl_io.c b/xs/src/admesh/stl_io.c
index 1b2671ab2..daa999b8d 100644
--- a/xs/src/admesh/stl_io.c
+++ b/xs/src/admesh/stl_io.c
@@ -121,7 +121,7 @@ Normals fixed         : %5d\n", stl->stats.normals_fixed);
 }
 
 void
-stl_write_ascii(stl_file *stl, char *file, char *label)
+stl_write_ascii(stl_file *stl, const char *file, const char *label)
 {
   int       i;
   FILE      *fp;
@@ -241,7 +241,7 @@ stl_put_little_float(FILE *fp, float value_in)
 
 
 void
-stl_write_binary(stl_file *stl, char *file, char *label)
+stl_write_binary(stl_file *stl, const char *file, const char *label)
 {
   FILE      *fp;
   int       i;
diff --git a/xs/xsp/TriangleMesh.xsp b/xs/xsp/TriangleMesh.xsp
index a41f3b098..df0b827b5 100644
--- a/xs/xsp/TriangleMesh.xsp
+++ b/xs/xsp/TriangleMesh.xsp
@@ -11,6 +11,8 @@
     TriangleMesh* clone()
         %code{% const char* CLASS = "Slic3r::TriangleMesh"; RETVAL = new TriangleMesh(*THIS); %};
     void ReadSTLFile(char* input_file);
+    void write_ascii(char* output_file);
+    void write_binary(char* output_file);
     void ReadFromPerl(SV* vertices, SV* facets);
     void repair();
     void WriteOBJFile(char* output_file);