diff --git a/src/serializers/GltfSerializer.cpp b/src/serializers/GltfSerializer.cpp
index 8b1c0ec03b..b8487a5fb7 100644
--- a/src/serializers/GltfSerializer.cpp
+++ b/src/serializers/GltfSerializer.cpp
@@ -106,7 +106,10 @@ int GltfSerializer::writeMaterial(const ifcopenshell::geometry::taxonomy::style:
 		base[3] = 1. - style->transparency;
 	}
 
-	json_["materials"].push_back({ {"name", style->name}, {"doubleSided", true}, {"pbrMetallicRoughness", {{"baseColorFactor", base}, {"metallicFactor", 0}}}});
+	if (style->has_specularity())
+		json_["materials"].push_back({ {"name", style->name}, {"doubleSided", true}, {"pbrMetallicRoughness", {{"baseColorFactor", base}, {"metallicFactor", 0}, {"roughnessFactor", 1.0 / style->specularity}}}});
+	else
+		json_["materials"].push_back({ {"name", style->name}, {"doubleSided", true}, {"pbrMetallicRoughness", {{"baseColorFactor", base}, {"metallicFactor", 0}}}});
 	
 	if (style->transparency == style->transparency && style->transparency > 1.e-9) {
 		json_["materials"].back()["alphaMode"] = "BLEND";