diff --git a/decor/optimistic_string_writer.go b/decor/optimistic_string_writer.go
deleted file mode 100644
index c6a3438..0000000
--- a/decor/optimistic_string_writer.go
+++ /dev/null
@@ -1,10 +0,0 @@
-package decor
-
-import "io"
-
-func mustWriteString(w io.Writer, s string) {
-	_, err := io.WriteString(w, s)
-	if err != nil {
-		panic(err)
-	}
-}
diff --git a/decor/percentage.go b/decor/percentage.go
index d39522f..5365842 100644
--- a/decor/percentage.go
+++ b/decor/percentage.go
@@ -23,11 +23,18 @@
 		}
 	}
 
-	mustWriteString(st, strconv.FormatFloat(float64(s), 'f', prec, 64))
+	p := bytePool.Get().(*[]byte)
+	b := strconv.AppendFloat(*p, float64(s), 'f', prec, 64)
 	if st.Flag(' ') {
-		mustWriteString(st, " ")
+		b = append(b, ' ', '%')
+	} else {
+		b = append(b, '%')
 	}
-	mustWriteString(st, "%")
+	_, err := st.Write(b)
+	bytePool.Put(p)
+	if err != nil {
+		panic(err)
+	}
 }
 
 // Percentage returns percentage decorator. It's a wrapper of NewPercentage.
diff --git a/decor/pool.go b/decor/pool.go
new file mode 100644
index 0000000..c8b3cc6
--- /dev/null
+++ b/decor/pool.go
@@ -0,0 +1,10 @@
+package decor
+
+import "sync"
+
+var bytePool = sync.Pool{
+	New: func() interface{} {
+		b := make([]byte, 0, 16)
+		return &b
+	},
+}
diff --git a/decor/size_type.go b/decor/size_type.go
index 09ecc23..c6205e8 100644
--- a/decor/size_type.go
+++ b/decor/size_type.go
@@ -49,11 +49,17 @@
 		unit = _iTiB
 	}
 
-	mustWriteString(st, strconv.FormatFloat(float64(self)/float64(unit), 'f', prec, 64))
+	p := bytePool.Get().(*[]byte)
+	b := strconv.AppendFloat(*p, float64(self)/float64(unit), 'f', prec, 64)
 	if st.Flag(' ') {
-		mustWriteString(st, " ")
+		b = append(b, ' ')
 	}
-	mustWriteString(st, unit.String())
+	b = append(b, []byte(unit.String())...)
+	_, err := st.Write(b)
+	bytePool.Put(p)
+	if err != nil {
+		panic(err)
+	}
 }
 
 const (
@@ -97,9 +103,15 @@
 		unit = _TB
 	}
 
-	mustWriteString(st, strconv.FormatFloat(float64(self)/float64(unit), 'f', prec, 64))
+	p := bytePool.Get().(*[]byte)
+	b := strconv.AppendFloat(*p, float64(self)/float64(unit), 'f', prec, 64)
 	if st.Flag(' ') {
-		mustWriteString(st, " ")
+		b = append(b, ' ')
 	}
-	mustWriteString(st, unit.String())
+	b = append(b, []byte(unit.String())...)
+	_, err := st.Write(b)
+	bytePool.Put(p)
+	if err != nil {
+		panic(err)
+	}
 }
diff --git a/decor/speed.go b/decor/speed.go
index f2ba691..e37302e 100644
--- a/decor/speed.go
+++ b/decor/speed.go
@@ -22,7 +22,10 @@
 
 func (self *speedFormatter) Format(st fmt.State, verb rune) {
 	self.Formatter.Format(st, verb)
-	mustWriteString(st, "/s")
+	_, err := st.Write([]byte("/s"))
+	if err != nil {
+		panic(err)
+	}
 }
 
 // EwmaSpeed exponential-weighted-moving-average based speed decorator.