diff --git a/README.md b/README.md
index a2a266f..feb0356 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,14 @@ socket << "\r\n"
 socket << form.to_s
 ```
 
+It's also possible to create a non-file part with Content-Type:
+
+``` ruby
+form = HTTP::FormData.create({
+  :username     => HTTP::FormData::Part.new('{"a": 1}', content_type: 'application/json'),
+  :avatar_file  => HTTP::FormData::File.new("/home/ixti/avatar.png")
+})
+```
 
 ## Supported Ruby Versions
 
diff --git a/lib/http/form_data.rb b/lib/http/form_data.rb
index 73749af..1a26906 100644
--- a/lib/http/form_data.rb
+++ b/lib/http/form_data.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "http/form_data/part"
 require "http/form_data/file"
 require "http/form_data/multipart"
 require "http/form_data/urlencoded"
diff --git a/lib/http/form_data/file.rb b/lib/http/form_data/file.rb
index adcf5de..3d4da02 100644
--- a/lib/http/form_data/file.rb
+++ b/lib/http/form_data/file.rb
@@ -18,12 +18,10 @@ module FormData
     # @example Usage with pathname
     #
     #  FormData::File.new "/home/ixti/avatar.png"
-    class File
+    class File < Part
       # Default MIME type
       DEFAULT_MIME = "application/octet-stream"
 
-      attr_reader :mime_type, :filename
-
       # @see DEFAULT_MIME
       # @param [String, StringIO, File] file_or_io Filename or IO instance.
       # @param [#to_h] opts
diff --git a/lib/http/form_data/multipart/param.rb b/lib/http/form_data/multipart/param.rb
index 32b9c90..fc63e06 100644
--- a/lib/http/form_data/multipart/param.rb
+++ b/lib/http/form_data/multipart/param.rb
@@ -5,19 +5,27 @@ module FormData
     class Multipart
       # Utility class to represent multi-part chunks
       class Param
-        CONTENT_DISPOSITION = ""
-
         # @param [#to_s] name
-        # @param [FormData::File, #to_s] value
+        # @param [FormData::File, FormData::Part, #to_s] value
         def initialize(name, value)
-          @name   = name.to_s
-          @value  = value
-          @header = "Content-Disposition: form-data; name=#{@name.inspect}"
+          @name = name.to_s
+
+          @part =
+            if value.is_a?(FormData::Part)
+              value
+            else
+              FormData::Part.new(value)
+            end
 
-          return unless file?
+          parameters = { :name => @name }
+          parameters[:filename] = @part.filename if @part.filename
+          parameters = parameters.map { |k, v| "#{k}=#{v.inspect}" }.join("; ")
 
-          @header = "#{@header}; filename=#{value.filename.inspect}#{CRLF}" \
-                    "Content-Type: #{value.mime_type}"
+          @header = "Content-Disposition: form-data; #{parameters}"
+
+          return unless @part.mime_type
+
+          @header += "#{CRLF}Content-Type: #{@part.mime_type}"
         end
 
         # Returns body part with headers and data.
@@ -37,20 +45,14 @@ def initialize(name, value)
         #
         # @return [String]
         def to_s
-          "#{@header}#{CRLF * 2}#{@value}"
+          "#{@header}#{CRLF * 2}#{@part}"
         end
 
         # Calculates size of a part (headers + body).
         #
         # @return [Fixnum]
         def size
-          size = @header.bytesize + (CRLF.bytesize * 2)
-
-          if file?
-            size + @value.size
-          else
-            size + @value.to_s.bytesize
-          end
+          @header.bytesize + (CRLF.bytesize * 2) + @part.size
         end
 
         # Flattens given `data` Hash into an array of `Param`'s.
@@ -70,15 +72,6 @@ def self.coerce(data)
 
           params
         end
-
-        private
-
-        # Tells whenever value is a {FormData::File} or not.
-        #
-        # @return [Boolean]
-        def file?
-          @value.is_a? FormData::File
-        end
       end
     end
   end
diff --git a/lib/http/form_data/part.rb b/lib/http/form_data/part.rb
new file mode 100644
index 0000000..89442aa
--- /dev/null
+++ b/lib/http/form_data/part.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module HTTP
+  module FormData
+    class Part
+      attr_reader :mime_type, :filename
+
+      # @param [#to_s] body
+      # @param [String] :mime_type
+      # @param [String] :filename
+      def initialize(body, mime_type: nil, filename: nil)
+        @body = body.to_s
+        @mime_type = mime_type
+        @filename = filename
+      end
+
+      # Returns content size.
+      #
+      # @return [Integer]
+      def size
+        @body.bytesize
+      end
+
+      # Returns content of a file of IO.
+      #
+      # @return [String]
+      def to_s
+        @body
+      end
+    end
+  end
+end
diff --git a/spec/lib/http/form_data/multipart_spec.rb b/spec/lib/http/form_data/multipart_spec.rb
index 8571fab..bd95614 100644
--- a/spec/lib/http/form_data/multipart_spec.rb
+++ b/spec/lib/http/form_data/multipart_spec.rb
@@ -41,5 +41,21 @@ def disposition(params)
         "--#{boundary_value}--"
       ].join("")
     end
+
+    context "with filename set to nil" do
+      let(:part) { HTTP::FormData::Part.new("s", :filename => nil) }
+      let(:form_data) { HTTP::FormData::Multipart.new(:foo => part) }
+
+      it "doesn't include a filename" do
+        boundary_value = form_data.content_type[/(#{boundary})$/, 1]
+
+        expect(form_data.to_s).to eq [
+          "--#{boundary_value}#{crlf}",
+          "#{disposition 'name' => 'foo'}#{crlf}",
+          "#{crlf}s#{crlf}",
+          "--#{boundary_value}--"
+        ].join("")
+      end
+    end
   end
 end
diff --git a/spec/lib/http/form_data/part_spec.rb b/spec/lib/http/form_data/part_spec.rb
new file mode 100644
index 0000000..b2e619b
--- /dev/null
+++ b/spec/lib/http/form_data/part_spec.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+RSpec.describe HTTP::FormData::Part do
+  let(:body) { "" }
+  let(:opts) { {} }
+
+  describe "#size" do
+    subject { described_class.new(body, opts).size }
+
+    context "when body given as a String" do
+      let(:body) { "привет мир!" }
+      it { is_expected.to eq 20 }
+    end
+  end
+
+  describe "#to_s" do
+    subject { described_class.new(body, opts).to_s }
+
+    context "when body given as String" do
+      let(:body) { "привет мир!" }
+      it { is_expected.to eq "привет мир!" }
+    end
+  end
+
+  describe "#filename" do
+    subject { described_class.new(body, opts).filename }
+
+    it { is_expected.to eq nil }
+
+    context "when it was given with options" do
+      let(:opts) { { :filename => "foobar.txt" } }
+      it { is_expected.to eq "foobar.txt" }
+    end
+  end
+
+  describe "#mime_type" do
+    subject { described_class.new(body, opts).mime_type }
+
+    it { is_expected.to eq nil }
+
+    context "when it was given with options" do
+      let(:opts) { { :mime_type => "application/json" } }
+      it { is_expected.to eq "application/json" }
+    end
+  end
+end