diff --git a/lib/glacier/string/str_format.h b/lib/glacier/string/str_format.h
index 3ce86bc..ca00e3e 100644
--- a/lib/glacier/string/str_format.h
+++ b/lib/glacier/string/str_format.h
@@ -59,10 +59,15 @@ void StrFormatInternal(StringBuilder& builder, StringView format, T value,
 }
 
 template <typename... Args>
-StringBuilder StrFormat(StringView format, Args... args) {
-  StringBuilder builder;
+String StrFormat(StringView format, Args... args) {
+  VariableStringBuilder builder;
+  StrFormatInternal(builder, format, args...);
+  return builder.ToString();
+}
+
+template <typename... Args>
+void StrFormat(StringBuilder& builder, StringView format, Args... args) {
   StrFormatInternal(builder, format, args...);
-  return glcr::Move(builder);
 }
 
 }  // namespace glcr
diff --git a/lib/glacier/string/string_builder.cpp b/lib/glacier/string/string_builder.cpp
index aa4d2d5..3b75e86 100644
--- a/lib/glacier/string/string_builder.cpp
+++ b/lib/glacier/string/string_builder.cpp
@@ -2,23 +2,29 @@
 
 namespace glcr {
 
-void StringBuilder::PushBack(const StringView& str) {
-  if (capacity() < size() + str.size()) {
-    uint64_t new_capacity = capacity() == 0 ? 1 : capacity() * 2;
+uint64_t VariableStringBuilder::size() const { return data_.size(); }
+
+void VariableStringBuilder::PushBack(const StringView& str) {
+  if (data_.capacity() < size() + str.size()) {
+    uint64_t new_capacity = data_.capacity() == 0 ? 1 : data_.capacity() * 2;
     while (new_capacity < size() + str.size()) {
       new_capacity *= 2;
     }
-    Resize(new_capacity);
+    data_.Resize(new_capacity);
   }
   for (uint64_t i = 0; i < str.size(); i++) {
-    Vector<char>::PushBack(str[i]);
+    data_.PushBack(str[i]);
   }
 }
 
-String StringBuilder::ToString() const { return String(RawPtr(), size()); }
+void VariableStringBuilder::PushBack(const char str) { data_.PushBack(str); }
 
-StringBuilder::operator StringView() const {
-  return StringView(RawPtr(), size());
+String VariableStringBuilder::ToString() const {
+  return String(data_.RawPtr(), size());
+}
+
+VariableStringBuilder::operator StringView() const {
+  return StringView(data_.RawPtr(), size());
 }
 
 }  // namespace glcr
diff --git a/lib/glacier/string/string_builder.h b/lib/glacier/string/string_builder.h
index 6e31bcb..2342033 100644
--- a/lib/glacier/string/string_builder.h
+++ b/lib/glacier/string/string_builder.h
@@ -6,21 +6,39 @@
 
 namespace glcr {
 
-class StringBuilder : public Vector<char> {
+class StringBuilder {
  public:
-  StringBuilder() : Vector<char>() {}
-  StringBuilder(const StringBuilder&) = delete;
-  StringBuilder(StringBuilder&& str) : Vector<char>(Move(str)) {}
+  virtual uint64_t size() const = 0;
+  virtual void PushBack(const StringView& str) = 0;
+  virtual void PushBack(const char str) = 0;
 
-  void PushBack(const StringView& str);
-  using Vector<char>::PushBack;
+  virtual String ToString() const = 0;
 
-  String ToString() const;
+  virtual operator StringView() const = 0;
+};
+
+class VariableStringBuilder : public StringBuilder {
+ public:
+  VariableStringBuilder() = default;
+  VariableStringBuilder(const VariableStringBuilder&) = delete;
+  VariableStringBuilder(VariableStringBuilder&&) = default;
+
+  ~VariableStringBuilder() = default;
+
+  virtual uint64_t size() const override;
+
+  virtual void PushBack(const StringView& str) override;
+  virtual void PushBack(const char str) override;
+
+  virtual String ToString() const override;
 
   // Note that this could become invalidated
   // at any time if more characters are pushed
   // onto the builder.
-  operator StringView() const;
+  virtual operator StringView() const override;
+
+ private:
+  Vector<char> data_;
 };
 
 }  // namespace glcr
diff --git a/lib/mammoth/include/mammoth/debug.h b/lib/mammoth/include/mammoth/debug.h
index 6cbc7d5..f06bf99 100644
--- a/lib/mammoth/include/mammoth/debug.h
+++ b/lib/mammoth/include/mammoth/debug.h
@@ -6,7 +6,7 @@
 #include <ztypes.h>
 
 // TODO: Take StringView here instead.
-void dbgln(const glcr::StringBuilder& builder);
+void dbgln(const glcr::String& string);
 
 template <typename... Args>
 void dbgln(const glcr::StringView& fmt, Args... args) {
diff --git a/lib/mammoth/src/debug.cpp b/lib/mammoth/src/debug.cpp
index f415ca2..337580c 100644
--- a/lib/mammoth/src/debug.cpp
+++ b/lib/mammoth/src/debug.cpp
@@ -3,10 +3,7 @@
 #include <glacier/status/error.h>
 #include <zcall.h>
 
-void dbgln(const glcr::StringBuilder& builder) {
-  glcr::String str = builder.ToString();
-  (void)ZDebug(str.cstr());
-}
+void dbgln(const glcr::String& string) { (void)ZDebug(string.cstr()); }
 
 void check(uint64_t code) {
   switch (code) {
diff --git a/zion/debug/debug.h b/zion/debug/debug.h
index c2fa9cc..aeace6f 100644
--- a/zion/debug/debug.h
+++ b/zion/debug/debug.h
@@ -11,6 +11,14 @@ void early_dbgln(const char* str);
 
 void dbgln(const glcr::StringView& str);
 
+// TODO: Write a version of StrFormat that
+// accepts a fix-sized buffer for output
+// to use in the kernel. That way we make
+// dbgln and panic calls without allocation.
+// Optionally, add a dbgln_unbounded method for
+// things like the Debug syscall where the formatted
+// string may be fairly large.
+
 template <typename... Args>
 void dbgln(const char* str, Args... args) {
   dbgln(glcr::StrFormat(str, args...));