diff --git a/instant-xml-macros/src/lib.rs b/instant-xml-macros/src/lib.rs
index 0bc8cc2..48e8e05 100644
--- a/instant-xml-macros/src/lib.rs
+++ b/instant-xml-macros/src/lib.rs
@@ -1,8 +1,8 @@
 extern crate proc_macro;
 
-use proc_macro::TokenStream;
+use proc_macro2::TokenStream;
 use quote::quote;
-use std::collections::HashMap;
+use std::collections::{BTreeSet, HashMap};
 use syn::{parse_macro_input, Lit, Meta, NestedMeta};
 
 const XML: &str = "xml";
@@ -54,60 +54,89 @@ impl<'a> Serializer {
         }
     }
 
-    fn add_header(&mut self, root_name: &str, output: &'a mut proc_macro2::TokenStream) {
-        output.extend(quote!(+ "<" + #root_name));
+    fn keys_set(&self) -> BTreeSet<&str> {
+        self.other_namespaces
+            .iter()
+            .map(|(k, _)| k.as_str())
+            .collect()
+    }
+
+    fn add_header(&mut self, root_name: &str, output: &'a mut TokenStream) {
+        output.extend(quote!(
+            serializer.output.write_char('<')?;
+            serializer.output.write_str(#root_name)?;
+        ));
 
         if let Some(default_namespace) = self.default_namespace.as_ref() {
-            output.extend(quote!(+ " xmlns=\"" + #default_namespace + "\""));
+            output.extend(quote!(
+                serializer.output.write_str(" xmlns=\"")?;
+                serializer.output.write_str(#default_namespace)?;
+                serializer.output.write_char('\"')?;
+            ));
         }
 
         let mut sorted_values: Vec<_> = self.other_namespaces.iter().collect();
         sorted_values.sort();
 
         for (key, val) in sorted_values {
-            output.extend(quote!(+ " xmlns:" + #key + "=\"" + #val + "\""));
+            output.extend(quote!(
+                serializer.output.write_str(" xmlns:")?;
+                serializer.output.write_str(#key)?;
+                serializer.output.write_str("=\"")?;
+                serializer.output.write_str(#val)?;
+                serializer.output.write_char('\"')?;
+            ));
         }
-
-        output.extend(quote!(+ ">"));
+        output.extend(quote!(
+            serializer.output.write_char('>')?;
+        ));
     }
 
-    fn add_footer(&mut self, root_name: &str, output: &'a mut proc_macro2::TokenStream) {
-        output.extend(quote!(+ "</" + #root_name + ">"));
+    fn add_footer(&mut self, root_name: &str, output: &'a mut TokenStream) {
+        output.extend(quote!(
+            serializer.output.write_str("</")?;
+            serializer.output.write_str(#root_name)?;
+            serializer.output.write_char('>')?;
+        ));
     }
 
     fn process_named_field(
         &mut self,
         field: &syn::Field,
-        output: &'a mut proc_macro2::TokenStream,
+        output: &'a mut TokenStream,
+        missing_prefixes: &'a mut BTreeSet<String>,
     ) {
-        let field_name = field.ident.as_ref().unwrap().to_string();
+        let name = field.ident.as_ref().unwrap().to_string();
         let field_value = field.ident.as_ref().unwrap();
-        let mut prefix = String::default();
+
+        output.extend(quote!(
+            let mut field = instant_xml::FieldContext {
+                name: #name,
+                attribute: None,
+            };
+        ));
 
         match Self::retrieve_field_attribute(field) {
-            Some(FieldAttribute::Namespace(namespace)) => {
-                output.extend(quote!(+ "<" + #field_name + " xmlns=\"" + #namespace + "\""));
+            Some(FieldAttribute::Namespace(namespace_key)) => {
+                output.extend(quote!(
+                    field.attribute = Some(instant_xml::FieldAttribute::Namespace(#namespace_key));
+                ));
             }
-            Some(FieldAttribute::PrefixIdentifier(prefix_key))
-                if !self.other_namespaces.is_empty() =>
-            {
-                match self.other_namespaces.get(&prefix_key) {
-                    Some(_) => {
-                        prefix = prefix_key + ":";
-                        output.extend(quote!(+ "<" + #prefix + #field_name));
-                    }
-                    None => todo!(), // return the error
+            Some(FieldAttribute::PrefixIdentifier(prefix_key)) => {
+                output.extend(quote!(
+                    field.attribute = Some(instant_xml::FieldAttribute::Prefix(#prefix_key));
+                ));
+
+                if self.other_namespaces.get(&prefix_key).is_none() {
+                    missing_prefixes.insert(prefix_key);
                 };
             }
-            _ => {
-                // Without the namespace
-                output.extend(quote!(+ "<" + #field_name));
-            }
+            _ => {}
         };
 
-        output.extend(
-            quote!(+ ">" + self.#field_value.to_string().as_str() + "</" + #prefix + #field_name + ">"),
-        );
+        output.extend(quote!(
+            self.#field_value.serialize(serializer, Some(&field))?;
+        ));
     }
 
     fn retrieve_namespace_list(attributes: &Vec<syn::Attribute>) -> Option<syn::MetaList> {
@@ -154,14 +183,15 @@ impl<'a> Serializer {
 }
 
 #[proc_macro_derive(ToXml, attributes(xml))]
-pub fn to_xml(input: TokenStream) -> TokenStream {
+pub fn to_xml(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let ast = parse_macro_input!(input as syn::DeriveInput);
-
     let ident = &ast.ident;
     let root_name = ident.to_string();
-    let mut output: proc_macro2::TokenStream = TokenStream::from(quote!("".to_owned())).into();
-
+    let mut missing_prefixes = BTreeSet::new();
     let mut serializer = Serializer::new(&ast.attrs);
+
+    let mut output = TokenStream::new();
+
     serializer.add_header(&root_name, &mut output);
 
     match &ast.data {
@@ -169,7 +199,7 @@ pub fn to_xml(input: TokenStream) -> TokenStream {
             match data.fields {
                 syn::Fields::Named(ref fields) => {
                     fields.named.iter().for_each(|field| {
-                        serializer.process_named_field(field, &mut output);
+                        serializer.process_named_field(field, &mut output, &mut missing_prefixes);
                     });
                 }
                 syn::Fields::Unnamed(_) => todo!(),
@@ -181,22 +211,50 @@ pub fn to_xml(input: TokenStream) -> TokenStream {
 
     serializer.add_footer(&root_name, &mut output);
 
-    TokenStream::from(quote!(
+    let current_prefixes = serializer.keys_set();
+    proc_macro::TokenStream::from(quote!(
         impl ToXml for #ident {
-            fn write_xml<W: ::std::fmt::Write>(&self, write: &mut W) -> Result<(), instant_xml::Error> {
-                write.write_str(&(#output))?;
+            fn serialize<W>(&self, serializer: &mut instant_xml::Serializer<W>, _field_data: Option<&instant_xml::FieldContext>) -> Result<(), instant_xml::Error>
+            where
+                W: std::fmt::Write,
+            {
+                let mut field_context = instant_xml::FieldContext {
+                    name: #root_name,
+                    attribute: None,
+                };
+
+                // Check if prefix exist
+                #(
+                    if serializer.parent_prefixes.get(#missing_prefixes).is_none() {
+                        return Err(instant_xml::Error::WrongPrefix);
+                    }
+                )*;
+
+                // Adding current prefixes
+                let mut to_remove: Vec<&str> = Vec::new();
+                #(if serializer.parent_prefixes.insert(#current_prefixes) {
+                    to_remove.push(#current_prefixes);
+                };)*;
+
+                #output
+
+                // Removing current prefixes
+                for it in to_remove {
+                    serializer.parent_prefixes.remove(it);
+                }
+
                 Ok(())
             }
-        }
+        };
     ))
 }
 
 #[proc_macro_derive(FromXml, attributes(xml))]
-pub fn from_xml(input: TokenStream) -> TokenStream {
+pub fn from_xml(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let ast = parse_macro_input!(input as syn::ItemStruct);
     let ident = &ast.ident;
     let name = ident.to_string();
-    TokenStream::from(quote!(
+    proc_macro::TokenStream::from(quote!(
         impl<'xml> FromXml<'xml> for #ident {
             fn from_xml(input: &str) -> Result<Self, ::instant_xml::Error> {
                 use ::instant_xml::parse::Parse;
diff --git a/instant-xml/src/lib.rs b/instant-xml/src/lib.rs
index 98facff..99f2c89 100644
--- a/instant-xml/src/lib.rs
+++ b/instant-xml/src/lib.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{BTreeSet, HashMap};
 use std::fmt;
 
 use thiserror::Error;
@@ -10,13 +10,175 @@ pub use macros::{FromXml, ToXml};
 pub mod parse;
 
 pub trait ToXml {
-    fn write_xml<W: fmt::Write>(&self, write: &mut W) -> Result<(), Error>;
-
     fn to_xml(&self) -> Result<String, Error> {
-        let mut out = String::new();
-        self.write_xml(&mut out)?;
-        Ok(out)
+        let mut output = String::new();
+        let mut serializer = Serializer::new(&mut output);
+        self.serialize(&mut serializer, None)?;
+        Ok(output)
     }
+
+    fn serialize<W>(
+        &self,
+        serializer: &mut Serializer<W>,
+        field_context: Option<&FieldContext>,
+    ) -> Result<(), Error>
+    where
+        W: fmt::Write;
+}
+
+macro_rules! to_xml_for_number {
+    ($typ:ty) => {
+        impl ToXml for $typ {
+            fn serialize<W>(
+                &self,
+                serializer: &mut Serializer<W>,
+                field_context: Option<&FieldContext>,
+            ) -> Result<(), Error>
+            where
+                W: fmt::Write,
+            {
+                match field_context {
+                    Some(field_context) => {
+                        serializer.add_open_tag(field_context)?;
+                        write!(serializer.output, "{}", &self)?;
+                        serializer.add_close_tag(field_context)?;
+                        Ok(())
+                    }
+                    None => Err(Error::UnexpectedValue),
+                }
+            }
+        }
+    };
+}
+
+to_xml_for_number!(i8);
+to_xml_for_number!(i16);
+to_xml_for_number!(i32);
+to_xml_for_number!(i64);
+to_xml_for_number!(u8);
+to_xml_for_number!(u16);
+to_xml_for_number!(u32);
+to_xml_for_number!(u64);
+
+impl ToXml for bool {
+    fn serialize<W>(
+        &self,
+        serializer: &mut Serializer<W>,
+        field_context: Option<&FieldContext>,
+    ) -> Result<(), Error>
+    where
+        W: fmt::Write,
+    {
+        let value = match self {
+            true => "true",
+            false => "false",
+        };
+
+        match field_context {
+            Some(field_context) => {
+                serializer.add_open_tag(field_context)?;
+                serializer.output.write_str(value)?;
+                serializer.add_close_tag(field_context)?;
+                Ok(())
+            }
+            None => Err(Error::UnexpectedValue),
+        }
+    }
+}
+
+impl ToXml for String {
+    fn serialize<W>(
+        &self,
+        serializer: &mut Serializer<W>,
+        field_context: Option<&FieldContext>,
+    ) -> Result<(), Error>
+    where
+        W: fmt::Write,
+    {
+        match field_context {
+            Some(field_context) => {
+                serializer.add_open_tag(field_context)?;
+                serializer.output.write_str(self)?;
+                serializer.add_close_tag(field_context)?;
+                Ok(())
+            }
+            None => Err(Error::UnexpectedValue),
+        }
+    }
+}
+
+pub struct Serializer<'xml, W>
+where
+    W: fmt::Write,
+{
+    #[doc(hidden)]
+    pub parent_prefixes: BTreeSet<&'xml str>,
+    #[doc(hidden)]
+    pub output: &'xml mut W,
+}
+
+impl<'xml, W: std::fmt::Write> Serializer<'xml, W> {
+    pub fn new(output: &'xml mut W) -> Self {
+        Self {
+            parent_prefixes: BTreeSet::new(),
+            output,
+        }
+    }
+
+    fn add_open_tag(&mut self, field_context: &FieldContext) -> Result<(), Error> {
+        match field_context.attribute {
+            Some(FieldAttribute::Prefix(prefix)) => {
+                self.output.write_char('<')?;
+                self.output.write_str(prefix)?;
+                self.output.write_char(':')?;
+                self.output.write_str(field_context.name)?;
+                self.output.write_char('>')?;
+            }
+            Some(FieldAttribute::Namespace(namespace)) => {
+                self.output.write_char('<')?;
+                self.output.write_str(field_context.name)?;
+                self.output.write_str(" xmlns=\"")?;
+                self.output.write_str(namespace)?;
+                self.output.write_str("\">")?;
+            }
+            _ => {
+                self.output.write_char('<')?;
+                self.output.write_str(field_context.name)?;
+                self.output.write_char('>')?;
+            }
+        }
+        Ok(())
+    }
+
+    fn add_close_tag(&mut self, field_context: &FieldContext) -> Result<(), Error> {
+        match field_context.attribute {
+            Some(FieldAttribute::Prefix(prefix)) => {
+                self.output.write_str("</")?;
+                self.output.write_str(prefix)?;
+                self.output.write_char(':')?;
+                self.output.write_str(field_context.name)?;
+                self.output.write_char('>')?;
+            }
+            _ => {
+                self.output.write_str("</")?;
+                self.output.write_str(field_context.name)?;
+                self.output.write_char('>')?;
+            }
+        }
+        Ok(())
+    }
+}
+
+pub enum FieldAttribute<'xml> {
+    Prefix(&'xml str),
+    Namespace(&'xml str),
+}
+
+pub struct FieldContext<'xml> {
+    #[doc(hidden)]
+    pub name: &'xml str,
+    #[doc(hidden)]
+    pub attribute: Option<FieldAttribute<'xml>>,
 }
 
 pub trait FromXml<'xml>: Sized {
@@ -40,4 +202,6 @@ pub enum Error {
     UnexpectedEndOfStream,
     #[error("unexpected value")]
     UnexpectedValue,
+    #[error("wrong prefix")]
+    WrongPrefix,
 }
diff --git a/instant-xml/tests/all.rs b/instant-xml/tests/all.rs
index f93efde..12282bc 100644
--- a/instant-xml/tests/all.rs
+++ b/instant-xml/tests/all.rs
@@ -3,6 +3,30 @@ use instant_xml::{FromXml, ToXml};
 #[derive(Debug, Eq, FromXml, PartialEq, ToXml)]
 struct Unit;
 
+#[derive(Debug, Eq, PartialEq, ToXml)]
+#[xml(namespace("URI", bar = "BAZ", foo = "BAR"))]
+struct StructWithCustomField {
+    test: Nested,
+}
+
+#[derive(Debug, Eq, PartialEq, ToXml)]
+struct Nested {
+    #[xml(namespace(bar))]
+    flag: bool,
+}
+
+#[derive(Debug, Eq, PartialEq, ToXml)]
+#[xml(namespace("URI", bar = "BAZ", foo = "BAR"))]
+struct StructWithCustomFieldWrongPrefix {
+    test: NestedWrongPrefix,
+}
+
+#[derive(Debug, Eq, PartialEq, ToXml)]
+struct NestedWrongPrefix {
+    #[xml(namespace(dar))]
+    flag: bool,
+}
+
 #[derive(Debug, Eq, PartialEq, ToXml)]
 #[xml(namespace("URI", bar = "BAZ", foo = "BAR"))]
 struct StructWithNamedFields {
@@ -32,3 +56,28 @@ fn struct_with_named_fields() {
         "<StructWithNamedFields xmlns=\"URI\" xmlns:bar=\"BAZ\" xmlns:foo=\"BAR\"><flag>true</flag><bar:string>test</bar:string><number xmlns=\"typo\">1</number></StructWithNamedFields>"
     );
 }
+
+#[test]
+fn struct_with_custom_field() {
+    assert_eq!(
+        StructWithCustomField {
+            test: Nested {
+                flag: true,
+            },
+        }
+        .to_xml()
+        .unwrap(),
+        "<StructWithCustomField xmlns=\"URI\" xmlns:bar=\"BAZ\" xmlns:foo=\"BAR\"><Nested><bar:flag>true</bar:flag></Nested></StructWithCustomField>"
+
+    );
+}
+
+#[test]
+#[should_panic]
+fn struct_with_custom_field_wrong_prefix() {
+    StructWithCustomFieldWrongPrefix {
+        test: NestedWrongPrefix { flag: true },
+    }
+    .to_xml()
+    .unwrap();
+}