diff --git a/2018/day05-1.go b/2018/day05-1.go
index ce3c281..4b8ee5a 100644
--- a/2018/day05-1.go
+++ b/2018/day05-1.go
@@ -1,50 +1,14 @@
 package main
 
 import (
-	"bytes"
 	"fmt"
 
+	"internal/polymer"
 	"internal/util"
 )
 
 func main() {
 	data := util.ReadInputBytes()
-	result := ApplyReactions(data)
+	result := polymer.ApplyReactions(data)
 	fmt.Println(len(result))
 }
-
-func ApplyReactions(data []byte) string {
-	result := data
-	changed := true
-
-	for changed {
-		result, changed = React1(result)
-	}
-
-	return string(result)
-}
-
-// React finds substrings of the form "xX" or "Xx" and removes them, returning
-// the resulting bytes.
-func React(data []byte) ([]byte, bool) {
-	result := bytes.Buffer{}
-	changed := false
-
-	for i := 0; i < len(data); i++ {
-		if i < len(data)-1 &&
-			data[i] != data[i+1] &&
-			string(bytes.ToLower([]byte{data[i]})) == string(bytes.ToLower([]byte{data[i+1]})) {
-
-			// we've found a reduction; skip over it without writing
-			//			return append(data[:i], data[i+2:]...), true
-			i++
-			changed = true
-			continue
-		}
-
-		result.WriteByte(data[i])
-	}
-
-	// No changes possible.
-	return result.Bytes(), changed
-}
diff --git a/2018/internal/polymer/polymer.go b/2018/internal/polymer/polymer.go
new file mode 100644
index 0000000..1ed77bd
--- /dev/null
+++ b/2018/internal/polymer/polymer.go
@@ -0,0 +1,42 @@
+// Functions for operating on polymers from day 5.
+package polymer
+
+import (
+	"bytes"
+)
+
+func ApplyReactions(data []byte) string {
+	result := data
+	changed := true
+
+	for changed {
+		result, changed = React(result)
+	}
+
+	return string(result)
+}
+
+// React finds substrings of the form "xX" or "Xx" and removes them, returning
+// the resulting bytes.
+func React(data []byte) ([]byte, bool) {
+	result := bytes.Buffer{}
+	changed := false
+
+	for i := 0; i < len(data); i++ {
+		if i < len(data)-1 &&
+			data[i] != data[i+1] &&
+			string(bytes.ToLower([]byte{data[i]})) == string(bytes.ToLower([]byte{data[i+1]})) {
+
+			// we've found a reduction; skip over it without writing
+			//			return append(data[:i], data[i+2:]...), true
+			i++
+			changed = true
+			continue
+		}
+
+		result.WriteByte(data[i])
+	}
+
+	// No changes possible.
+	return result.Bytes(), changed
+}