diff --git a/excelize.go b/excelize.go
index bc37c0a..3c81db2 100644
--- a/excelize.go
+++ b/excelize.go
@@ -4,6 +4,9 @@ import (
 	"archive/zip"
 	"bytes"
 	"encoding/xml"
+	"io"
+	"io/ioutil"
+	"os"
 	"strconv"
 	"strings"
 )
@@ -19,20 +22,31 @@ type File struct {
 // OpenFile take the name of an XLSX file and returns a populated XLSX file
 // struct for it.
 func OpenFile(filename string) (*File, error) {
-	var f *zip.ReadCloser
-	var err error
-	file := make(map[string]string)
-	c := make(map[string]bool)
-	sheetCount := 0
-	f, err = zip.OpenReader(filename)
+	file, err := os.Open(filename)
 	if err != nil {
-		return &File{}, err
+		return nil, err
+	}
+	b, err := ioutil.ReadAll(file)
+	if err != nil {
+		return nil, err
+	}
+	return OpenReader(bytes.NewReader(b), int64(len(b)))
+}
+
+// OpenReader take an io.Reader and return a populated XLSX file.
+func OpenReader(r io.ReaderAt, size int64) (*File, error) {
+	zr, err := zip.NewReader(r, size)
+	if err != nil {
+		return nil, err
+	}
+	file, sheetCount, err := ReadZipReader(zr)
+	if err != nil {
+		return nil, err
 	}
-	file, sheetCount, _ = ReadZip(f)
 	return &File{
-		checked:    c,
+		checked:    make(map[string]bool),
 		XLSX:       file,
-		Path:       filename,
+		Path:       "",
 		SheetCount: sheetCount,
 	}, nil
 }
diff --git a/file.go b/file.go
index 2a044f0..17a8bba 100644
--- a/file.go
+++ b/file.go
@@ -3,6 +3,8 @@ package excelize
 import (
 	"archive/zip"
 	"bytes"
+	"fmt"
+	"io"
 	"os"
 )
 
@@ -29,53 +31,45 @@ func CreateFile() *File {
 
 // Save provides function to override the xlsx file with origin path.
 func (f *File) Save() error {
-	buf := new(bytes.Buffer)
-	w := zip.NewWriter(buf)
-	for path, content := range f.XLSX {
-		f, err := w.Create(path)
-		if err != nil {
-			return err
-		}
-		_, err = f.Write([]byte(content))
-		if err != nil {
-			return err
-		}
+	if f.Path == "" {
+		return fmt.Errorf("No path defined for file, consider File.WriteTo or File.Write")
 	}
-	err := w.Close()
-	if err != nil {
-		return err
-	}
-	file, err := os.OpenFile(f.Path, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0666)
-	if err != nil {
-		return err
-	}
-	buf.WriteTo(file)
-	return err
+	return f.WriteTo(f.Path)
 }
 
 // WriteTo provides function to create or update to an xlsx file at the provided
 // path.
 func (f *File) WriteTo(name string) error {
-	buf := new(bytes.Buffer)
-	w := zip.NewWriter(buf)
-	for path, content := range f.XLSX {
-		f, err := w.Create(path)
-		if err != nil {
-			return err
-		}
-		_, err = f.Write([]byte(content))
-		if err != nil {
-			return err
-		}
-	}
-	err := w.Close()
-	if err != nil {
-		return err
-	}
 	file, err := os.OpenFile(name, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0666)
 	if err != nil {
 		return err
 	}
-	buf.WriteTo(file)
-	return err
+	defer file.Close()
+	return f.Write(file)
+}
+
+// Write provides function to write to an io.Writer.
+func (f *File) Write(w io.Writer) error {
+	buf := new(bytes.Buffer)
+	zw := zip.NewWriter(buf)
+	for path, content := range f.XLSX {
+		fi, err := zw.Create(path)
+		if err != nil {
+			return err
+		}
+		_, err = fi.Write([]byte(content))
+		if err != nil {
+			return err
+		}
+	}
+	err := zw.Close()
+	if err != nil {
+		return err
+	}
+
+	if _, err := buf.WriteTo(w); err != nil {
+		return err
+	}
+
+	return nil
 }
diff --git a/lib.go b/lib.go
index c3767e3..8c56f1b 100644
--- a/lib.go
+++ b/lib.go
@@ -8,14 +8,6 @@ import (
 	"math"
 )
 
-// ReadZip takes a pointer to a zip.ReadCloser and returns a xlsx.File struct
-// populated with its contents. In most cases ReadZip is not used directly, but
-// is called internally by OpenFile.
-func ReadZip(f *zip.ReadCloser) (map[string]string, int, error) {
-	defer f.Close()
-	return ReadZipReader(&f.Reader)
-}
-
 // ReadZipReader can be used to read an XLSX in memory without touching the
 // filesystem.
 func ReadZipReader(r *zip.Reader) (map[string]string, int, error) {