diff --git a/README.md b/README.md
index a298ec85..167c3f33 100644
--- a/README.md
+++ b/README.md
@@ -200,7 +200,7 @@ The author of the Silk icon set is Mark James.
         --top-solid-layers  Number of solid layers to do for top surfaces (range: 0+, default: 3)
         --bottom-solid-layers  Number of solid layers to do for bottom surfaces (range: 0+, default: 3)
         --solid-layers      Shortcut for setting the two options above at once
-        --fill-density      Infill density (range: 0-1, default: 0.4)
+        --fill-density      Infill density (range: 0%-100%, default: 40%)
         --fill-angle        Infill angle in degrees (range: 0-90, default: 45)
         --fill-pattern      Pattern to use to fill non-solid layers (default: honeycomb)
         --solid-fill-pattern Pattern to use to fill solid layers (default: rectilinear)
diff --git a/lib/Slic3r/Config.pm b/lib/Slic3r/Config.pm
index e8884d6a..22088ff3 100644
--- a/lib/Slic3r/Config.pm
+++ b/lib/Slic3r/Config.pm
@@ -119,6 +119,11 @@ sub _handle_legacy {
     if ($opt_key eq 'gcode_flavor' && $value eq 'makerbot') {
         $value = 'makerware';
     }
+    if ($opt_key eq 'fill_density' && $value <= 1) {
+        # fill_density was turned into a percent value
+        $value *= 100;
+        $value = "$value";  # force update of the PV value, workaround for bug https://rt.cpan.org/Ticket/Display.html?id=94110
+    }
     
     # For historical reasons, the world's full of configs having these very low values;
     # to avoid unexpected behavior we need to ignore them.  Banning these two hard-coded
@@ -258,9 +263,9 @@ sub validate {
     
     # --fill-density
     die "Invalid value for --fill-density\n"
-        if $self->fill_density < 0 || $self->fill_density > 1;
+        if $self->fill_density < 0 || $self->fill_density > 100;
     die "The selected fill pattern is not supposed to work at 100% density\n"
-        if $self->fill_density == 1
+        if $self->fill_density == 100
             && !first { $_ eq $self->fill_pattern } @{$Options->{solid_fill_pattern}{values}};
     
     # --infill-every-layers
@@ -343,10 +348,11 @@ sub validate {
             @values = ($self->$opt_key);
         }
         foreach my $value (@values) {
-            if ($type eq 'i' || $type eq 'f') {
+            if ($type eq 'i' || $type eq 'f' || $opt->{type} eq 'percent') {
+                $value =~ s/%$// if $opt->{type} eq 'percent';
                 die "Invalid value for $opt_key\n"
                     if ($type eq 'i' && $value !~ /^-?\d+$/)
-                    || ($type eq 'f' && $value !~ /^-?(?:\d+|\d*\.\d+)$/)
+                    || (($type eq 'f' || $opt->{type} eq 'percent') && $value !~ /^-?(?:\d+|\d*\.\d+)$/)
                     || (defined $opt->{min} && $value < $opt->{min})
                     || (defined $opt->{max} && $value > $opt->{max});
             } elsif ($type eq 's' && $opt->{type} eq 'select') {
diff --git a/lib/Slic3r/Fill.pm b/lib/Slic3r/Fill.pm
index 43a88120..968b27f6 100644
--- a/lib/Slic3r/Fill.pm
+++ b/lib/Slic3r/Fill.pm
@@ -192,7 +192,7 @@ sub make_fill {
         
         # force 100% density and rectilinear fill for external surfaces
         if ($surface->surface_type != S_TYPE_INTERNAL) {
-            $density = 1;
+            $density = 100;
             $filler = $layerm->config->solid_fill_pattern;
             if ($is_bridge) {
                 $filler = 'rectilinear';
@@ -209,7 +209,7 @@ sub make_fill {
         $f->angle($layerm->config->fill_angle);
         my ($params, @polylines) = $f->fill_surface(
             $surface,
-            density => $density,
+            density => $density/100,
             flow    => $flow,
         );
         next unless @polylines;
diff --git a/lib/Slic3r/GUI/OptionsGroup.pm b/lib/Slic3r/GUI/OptionsGroup.pm
index d849405b..c1cbe2d1 100644
--- a/lib/Slic3r/GUI/OptionsGroup.pm
+++ b/lib/Slic3r/GUI/OptionsGroup.pm
@@ -165,7 +165,7 @@ sub _build_field {
     
     my $field;
     my $tooltip = $opt->{tooltip};
-    if ($opt->{type} =~ /^(i|f|s|s@)$/) {
+    if ($opt->{type} =~ /^(i|f|s|s@|percent)$/) {
         my $style = 0;
         $style = wxTE_MULTILINE if $opt->{multiline};
         # default width on Windows is too large
diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 68c31969..bc0c358b 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -604,7 +604,7 @@ sub bridge_over_infill {
     
     for my $region_id (0..$#{$self->print->regions}) {
         my $fill_density = $self->print->regions->[$region_id]->config->fill_density;
-        next if $fill_density == 1 || $fill_density == 0;
+        next if $fill_density == 100 || $fill_density == 0;
         
         for my $layer_id (1..$#{$self->layers}) {
             my $layer       = $self->layers->[$layer_id];
diff --git a/slic3r.pl b/slic3r.pl
index f633d69c..284f9169 100755
--- a/slic3r.pl
+++ b/slic3r.pl
@@ -301,7 +301,7 @@ $j
     --top-solid-layers  Number of solid layers to do for top surfaces (range: 0+, default: $config->{top_solid_layers})
     --bottom-solid-layers  Number of solid layers to do for bottom surfaces (range: 0+, default: $config->{bottom_solid_layers})
     --solid-layers      Shortcut for setting the two options above at once
-    --fill-density      Infill density (range: 0-1, default: $config->{fill_density})
+    --fill-density      Infill density (range: 0%-100%, default: $config->{fill_density}%)
     --fill-angle        Infill angle in degrees (range: 0-90, default: $config->{fill_angle})
     --fill-pattern      Pattern to use to fill non-solid layers (default: $config->{fill_pattern})
     --solid-fill-pattern Pattern to use to fill solid layers (default: $config->{solid_fill_pattern})
diff --git a/t/fill.t b/t/fill.t
index 55116016..365d8e06 100644
--- a/t/fill.t
+++ b/t/fill.t
@@ -172,7 +172,7 @@ for my $pattern (qw(rectilinear honeycomb hilbertcurve concentric)) {
     $config->set('fill_pattern', $pattern);
     $config->set('perimeters', 1);
     $config->set('skirts', 0);
-    $config->set('fill_density', 0.2);
+    $config->set('fill_density', 20);
     $config->set('layer_height', 0.05);
     $config->set('perimeter_extruder', 1);
     $config->set('infill_extruder', 2);
diff --git a/xs/src/Config.cpp b/xs/src/Config.cpp
index a4e2def8..6f59290b 100644
--- a/xs/src/Config.cpp
+++ b/xs/src/Config.cpp
@@ -95,6 +95,8 @@ ConfigBase::get(t_config_option_key opt_key) {
     if (opt == NULL) return &PL_sv_undef;
     if (ConfigOptionFloat* optv = dynamic_cast<ConfigOptionFloat*>(opt)) {
         return newSVnv(optv->value);
+    } else if (ConfigOptionPercent* optv = dynamic_cast<ConfigOptionPercent*>(opt)) {
+        return newSVnv(optv->value);
     } else if (ConfigOptionFloats* optv = dynamic_cast<ConfigOptionFloats*>(opt)) {
         AV* av = newAV();
         av_fill(av, optv->values.size()-1);
@@ -257,6 +259,8 @@ DynamicConfig::option(const t_config_option_key opt_key, bool create) {
                 opt = new ConfigOptionString ();
             } else if (optdef->type == coStrings) {
                 opt = new ConfigOptionStrings ();
+            } else if (optdef->type == coPercent) {
+                opt = new ConfigOptionPercent ();
             } else if (optdef->type == coFloatOrPercent) {
                 opt = new ConfigOptionFloatOrPercent ();
             } else if (optdef->type == coPoint) {
diff --git a/xs/src/Config.hpp b/xs/src/Config.hpp
index 9dcb4983..d5f280f2 100644
--- a/xs/src/Config.hpp
+++ b/xs/src/Config.hpp
@@ -181,6 +181,30 @@ class ConfigOptionStrings : public ConfigOption, public ConfigOptionVector<std::
     };
 };
 
+class ConfigOptionPercent : public ConfigOption
+{
+    public:
+    double value;
+    ConfigOptionPercent() : value(0) {};
+    
+    double get_abs_value(double ratio_over) const {
+        return ratio_over * this->value / 100;
+    };
+    
+    std::string serialize() const {
+        std::ostringstream ss;
+        ss << this->value;
+        std::string s(ss.str());
+        s += "%";
+        return s;
+    };
+    
+    void deserialize(std::string str) {
+        // don't try to parse the trailing % since it's optional
+        sscanf(str.c_str(), "%lf", &this->value);
+    };
+};
+
 class ConfigOptionFloatOrPercent : public ConfigOption
 {
     public:
@@ -360,6 +384,7 @@ enum ConfigOptionType {
     coInts,
     coString,
     coStrings,
+    coPercent,
     coFloatOrPercent,
     coPoint,
     coPoints,
diff --git a/xs/src/PrintConfig.hpp b/xs/src/PrintConfig.hpp
index fe0c6ce8..b9fce0e6 100644
--- a/xs/src/PrintConfig.hpp
+++ b/xs/src/PrintConfig.hpp
@@ -241,11 +241,12 @@ class PrintConfigDef
         Options["fill_angle"].cli = "fill-angle=i";
         Options["fill_angle"].max = 359;
 
-        Options["fill_density"].type = coFloat;
+        Options["fill_density"].type = coPercent;
         Options["fill_density"].label = "Fill density";
         Options["fill_density"].category = "Infill";
-        Options["fill_density"].tooltip = "Density of internal infill, expressed in the range 0 - 1.";
-        Options["fill_density"].cli = "fill-density=f";
+        Options["fill_density"].tooltip = "Density of internal infill, expressed in the range 0% - 100%.";
+        Options["fill_density"].sidetext = "%";
+        Options["fill_density"].cli = "fill-density=s";
 
         Options["fill_pattern"].type = coEnum;
         Options["fill_pattern"].label = "Fill pattern";
@@ -962,7 +963,7 @@ class PrintRegionConfig : public virtual StaticConfig
     ConfigOptionInt                 bottom_solid_layers;
     ConfigOptionBool                extra_perimeters;
     ConfigOptionInt                 fill_angle;
-    ConfigOptionFloat               fill_density;
+    ConfigOptionPercent             fill_density;
     ConfigOptionEnum<InfillPattern> fill_pattern;
     ConfigOptionInt                 infill_extruder;
     ConfigOptionFloatOrPercent      infill_extrusion_width;
@@ -984,7 +985,7 @@ class PrintRegionConfig : public virtual StaticConfig
         this->bottom_solid_layers.value                          = 3;
         this->extra_perimeters.value                             = true;
         this->fill_angle.value                                   = 45;
-        this->fill_density.value                                 = 0.4;
+        this->fill_density.value                                 = 40;
         this->fill_pattern.value                                 = ipHoneycomb;
         this->infill_extruder.value                              = 1;
         this->infill_extrusion_width.value                       = 0;
diff --git a/xs/xsp/Config.xsp b/xs/xsp/Config.xsp
index 1e59eb00..7b611b39 100644
--- a/xs/xsp/Config.xsp
+++ b/xs/xsp/Config.xsp
@@ -131,6 +131,8 @@ print_config_def()
             const char* opt_type;
             if (optdef->type == coFloat || optdef->type == coFloats || optdef->type == coFloatOrPercent) {
                 opt_type = "f";
+            } else if (optdef->type == coPercent) {
+                opt_type = "percent";
             } else if (optdef->type == coInt || optdef->type == coInts) {
                 opt_type = "i";
             } else if (optdef->type == coString) {