diff --git a/src/libslic3r/Format/3mf.cpp b/src/libslic3r/Format/3mf.cpp
index edf55ba37e..3612e6898c 100644
--- a/src/libslic3r/Format/3mf.cpp
+++ b/src/libslic3r/Format/3mf.cpp
@@ -86,6 +86,7 @@ const char* OBJECTID_ATTR = "objectid";
 const char* TRANSFORM_ATTR = "transform";
 const char* PRINTABLE_ATTR = "printable";
 const char* INSTANCESCOUNT_ATTR = "instances_count";
+const char* CUSTOM_SUPPORTS_ATTR = "slic3rpe:custom_supports";
 
 const char* KEY_ATTR = "key";
 const char* VALUE_ATTR = "value";
@@ -283,6 +284,7 @@ namespace Slic3r {
         {
             std::vector<float> vertices;
             std::vector<unsigned int> triangles;
+            std::vector<std::string> custom_supports;
 
             bool empty()
             {
@@ -293,6 +295,7 @@ namespace Slic3r {
             {
                 vertices.clear();
                 triangles.clear();
+                custom_supports.clear();
             }
         };
 
@@ -1539,6 +1542,8 @@ namespace Slic3r {
         m_curr_object.geometry.triangles.push_back((unsigned int)get_attribute_value_int(attributes, num_attributes, V1_ATTR));
         m_curr_object.geometry.triangles.push_back((unsigned int)get_attribute_value_int(attributes, num_attributes, V2_ATTR));
         m_curr_object.geometry.triangles.push_back((unsigned int)get_attribute_value_int(attributes, num_attributes, V3_ATTR));
+
+        m_curr_object.geometry.custom_supports.push_back(get_attribute_value_string(attributes, num_attributes, CUSTOM_SUPPORTS_ATTR));
         return true;
     }
 
@@ -1872,6 +1877,13 @@ namespace Slic3r {
                 volume->source.transform = Slic3r::Geometry::Transformation(volume_matrix_to_object);
             volume->calculate_convex_hull();
 
+            // recreate custom supports from previously loaded attribute
+            assert(geometry.custom_supports.size() == triangles_count);
+            for (unsigned i=0; i<triangles_count; ++i) {
+                if (! geometry.custom_supports[i].empty())
+                    volume->m_supported_facets.set_triangle_from_string(i, geometry.custom_supports[i]);
+            }
+
             // apply the remaining volume's metadata
             for (const Metadata& metadata : volume_data.metadata)
             {
@@ -2383,6 +2395,11 @@ namespace Slic3r {
                 {
                     stream << "v" << j + 1 << "=\"" << its.indices[i][j] + volume_it->second.first_vertex_id << "\" ";
                 }
+
+                std::string custom_supports_data_string = volume->m_supported_facets.get_triangle_as_string(i);
+                if (! custom_supports_data_string.empty())
+                    stream << CUSTOM_SUPPORTS_ATTR << "=\"" << custom_supports_data_string << "\" ";
+
                 stream << "/>\n";
             }
         }
diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index 4ff0a5c1bf..3beb74f235 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -1862,6 +1862,64 @@ void FacetsAnnotation::clear()
 
 
 
+// Following function takes data from a triangle and encodes it as string
+// of hexadecimal numbers (one digit per triangle). Used for 3MF export,
+// changing it may break backwards compatibility !!!!!
+std::string FacetsAnnotation::get_triangle_as_string(int triangle_idx) const
+{
+    std::string out;
+
+    auto triangle_it = m_data.find(triangle_idx);
+    if (triangle_it != m_data.end()) {
+        const std::vector<bool>& code = triangle_it->second;
+        int offset = 0;
+        while (offset < int(code.size())) {
+            int next_code = 0;
+            for (int i=3; i>=0; --i) {
+                next_code = next_code << 1;
+                next_code |= int(code[offset + i]);
+            }
+            offset += 4;
+
+            assert(next_code >=0 && next_code <= 15);
+            char digit = next_code < 10 ? next_code + '0' : (next_code-10)+'A';
+            out.insert(out.begin(), digit);
+        }
+    }
+    return out;
+}
+
+
+
+// Recover triangle splitting & state from string of hexadecimal values previously
+// generated by get_triangle_as_string. Used to load from 3MF.
+void FacetsAnnotation::set_triangle_from_string(int triangle_id, const std::string& str)
+{
+    assert(! str.empty());
+    m_data[triangle_id] = std::vector<bool>(); // zero current state or create new
+    std::vector<bool>& code = m_data[triangle_id];
+
+    for (auto it = str.crbegin(); it != str.crend(); ++it) {
+        const char ch = *it;
+        int dec = 0;
+        if (ch >= '0' && ch<='9')
+            dec = int(ch - '0');
+        else if (ch >='A' && ch <= 'F')
+            dec = 10 + int(ch - 'A');
+        else
+            assert(false);
+
+        // Convert to binary and append into code.
+        for (int i=0; i<4; ++i) {
+            code.insert(code.end(), bool(dec & (1 << i)));
+        }
+    }
+
+
+}
+
+
+
 // Test whether the two models contain the same number of ModelObjects with the same set of IDs
 // ordered in the same order. In that case it is not necessary to kill the background processing.
 bool model_object_list_equal(const Model &model_old, const Model &model_new)
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index 16f3f00ad5..92dc84d17a 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -409,6 +409,8 @@ public:
     bool set(const TriangleSelector& selector);
     indexed_triangle_set get_facets(const ModelVolume& mv, FacetSupportType type) const;
     void clear();
+    std::string get_triangle_as_string(int i) const;
+    void set_triangle_from_string(int triangle_id, const std::string& str);
 
     ClockType::time_point get_timestamp() const { return timestamp; }
     bool is_same_as(const FacetsAnnotation& other) const {
diff --git a/src/libslic3r/TriangleSelector.cpp b/src/libslic3r/TriangleSelector.cpp
index 50d775ed86..763bf58616 100644
--- a/src/libslic3r/TriangleSelector.cpp
+++ b/src/libslic3r/TriangleSelector.cpp
@@ -603,6 +603,7 @@ void TriangleSelector::deserialize(const std::map<int, std::vector<bool>> data)
     reset(); // dump any current state
     for (const auto& [triangle_id, code] : data) {
         assert(triangle_id < int(m_triangles.size()));
+        assert(! code.empty());
         int processed_triangles = 0;
         struct ProcessingInfo {
             int facet_id = 0;