diff --git a/example/main.ml b/example/main.ml
index e5645f3..674c3f4 100644
--- a/example/main.ml
+++ b/example/main.ml
@@ -1,3 +1,5 @@
+open Eio
+
 let ( / ) = Eio.Path.( / )
 
 module L = Eio_mem.Low_level
@@ -5,12 +7,8 @@ module L = Eio_mem.Low_level
 let () =
   Eio_main.run @@ fun e ->
   Eio_mem.run @@ fun env ->
-  let () =
-    Eio.Path.with_open_out ~create:(`If_missing 0o644) (env#fs / "hello.txt")
-    @@ fun flow ->
-    let fd = Eio_mem.Resource.fd_opt flow |> Option.get in
-    let nfd = L.dup fd in
-    let _ : int = L.writev nfd [ Cstruct.of_string "Hello, World" ] in
-    ()
-  in
-  Eio.traceln "Got: %s" (Eio.Path.load (env#fs / "hello.txt"))
+  Eio.Switch.run @@ fun sw ->
+  let r, w = L.pipe sw in
+  let _ : int = L.writev w [ Cstruct.of_string "Hello, world!" ] in
+  L.close w;
+  Eio.Flow.copy (Eio_mem.Flow.of_fd r) e#stdout
diff --git a/src/eio_mem.ml b/src/eio_mem.ml
index cbc83f6..c7243a3 100644
--- a/src/eio_mem.ml
+++ b/src/eio_mem.ml
@@ -17,6 +17,7 @@
 open Eio.Std
 module Resource = Resource
 module Low_level = Low_level
+module Flow = Flow
 
 module Fs = struct
   module Config = struct
@@ -92,7 +93,7 @@ module Fs = struct
         if Filename.is_relative path then Filename.concat t.dir_path path
         else path
       in
-      let d = v ~label ~path:full_path (Low_level.Dir.Dir_fd fd) in
+      let d = v ~label ~path:full_path (Low_level.Dir.Dir_fd fd.fd) in
       Eio.Resource.T (d, Handler.v)
 
     let chown ~follow:_ ?uid:_ ?gid:_ _t _p = ()
diff --git a/src/eio_mem.mli b/src/eio_mem.mli
index 1c512b1..648c0c2 100644
--- a/src/eio_mem.mli
+++ b/src/eio_mem.mli
@@ -23,6 +23,7 @@ module Fs : sig
 end
 
 module Low_level = Low_level
+module Flow = Flow
 
 module Resource : sig
   type 'a t = ([> `Mem_fd ] as 'a) Eio.Resource.t
diff --git a/src/low_level.ml b/src/low_level.ml
index 55cc050..362be8a 100644
--- a/src/low_level.ml
+++ b/src/low_level.ml
@@ -67,21 +67,7 @@ module Error = struct
     raise exn
 end
 
-module Fd : sig
-  type t = private int
-
-  val pp : t Fmt.t
-  val compare : t -> t -> int
-  val of_int : int -> t
-  val incr : t -> t
-end = struct
-  type t = int
-
-  let pp ppf i = Fmt.pf ppf "fd-%i" i
-  let compare (f1 : t) (f2 : t) = Int.compare (f1 :> int) (f2 :> int)
-  let of_int i = i
-  let incr t = t + 1
-end
+module Fd_table = Map.Make (Int)
 
 module Inode = struct
   type t = int64
@@ -99,7 +85,7 @@ end
 
 module Dir = struct
   type 'a t = { name : string; stat : Eio.File.Stat.t; entries : 'a list }
-  type fd = Fs | Cwd | Dir_fd of Fd.t
+  type fd = Fs | Cwd | Dir_fd of Int.t
 
   let make ~parent name stat =
     { name; stat; entries = [ (stat.ino, "."); (parent, "..") ] }
@@ -116,7 +102,17 @@ module Symlink = struct
   let make ~link_to name stat = { name; stat; link_to }
 end
 
-module Fd_table = Map.Make (Fd)
+module Pipe = struct
+  type t = { mutable closed : bool; chunks : Cstruct.t option Eio.Stream.t }
+
+  let make () = { closed = false; chunks = Eio.Stream.create max_int }
+  let write t buf = Eio.Stream.add t.chunks (Some buf)
+  let read t = Eio.Stream.take t.chunks
+
+  let close t =
+    t.closed <- true;
+    Eio.Stream.add t.chunks None
+end
 
 module Resource = struct
   type t =
@@ -126,11 +122,13 @@ module Resource = struct
     | File of File.t
     | Dir of (Inode.t * string) Dir.t
     | Symlink of Symlink.t
+    | Pipe of Pipe.t
 
   let pp ppf = function
     | Stdin -> Fmt.string ppf "stdin"
     | Stdout -> Fmt.string ppf "stdout"
     | Stderr -> Fmt.string ppf "stderr"
+    | Pipe _ -> Fmt.string ppf "pipe"
     | File f ->
         Fmt.pf ppf "file:%s:[%a]" f.name
           Fmt.(truncated ~max:12)
@@ -165,6 +163,70 @@ end
 
 type resource = Resource.t
 
+let std_table =
+  let open Resource in
+  Fd_table.add 0 (ref Stdin) Fd_table.empty
+  |> Fd_table.add 1 (ref Stdout)
+  |> Fd_table.add 2 (ref Stderr)
+
+let fd_table : resource ref Fd_table.t ref = ref std_table
+
+let update_fd_table_with_result fn =
+  let v, new_fd_table = fn !fd_table in
+  fd_table := new_fd_table;
+  v
+
+let update_fd_table fn =
+  let () = update_fd_table_with_result (fun fd -> ((), fn fd)) in
+  ()
+
+module Fd : sig
+  type t = { fd : int; mutable hook : Eio.Switch.hook }
+
+  val pp : t Fmt.t
+  val compare : t -> t -> int
+  val of_int_no_switch : int -> t
+  val of_int : sw:Eio.Switch.t -> int -> t
+  val incr : sw:Eio.Switch.t -> t -> t
+  val close : t -> unit
+end = struct
+  type t = { fd : int; mutable hook : Eio.Switch.hook }
+
+  let pp ppf t = Fmt.pf ppf "fd-%i" t.fd
+  let compare (f1 : t) (f2 : t) = Int.compare f1.fd f2.fd
+
+  let close fd =
+    Eio.Switch.remove_hook fd.hook;
+    update_fd_table @@ fun fds ->
+    match Fd_table.find_opt fd.fd fds with
+    | None -> Error.badf ~msg:"close" ()
+    | Some r -> (
+        match !r with
+        | Pipe p ->
+            Pipe.close p;
+            Fd_table.remove fd.fd fds
+        | _ -> Fd_table.remove fd.fd fds)
+
+  let of_int_no_switch fd = { fd; hook = Eio.Switch.null_hook }
+
+  let of_int ~sw fd =
+    let v = of_int_no_switch fd in
+    v.hook <- Eio.Switch.on_release_cancellable sw (fun () -> close v);
+    v
+
+  let incr ~sw t = of_int ~sw (t.fd + 1)
+end
+
+module Fd_tbl = struct
+  include Map.Make (Int)
+
+  let find_opt fd tbl = find_opt fd.Fd.fd tbl
+  let find' = find
+  let find fd tbl = find fd.Fd.fd tbl
+  let add k v tbl = add k.Fd.fd v tbl
+  let remove k tbl = remove k.Fd.fd tbl
+end
+
 let get_dir ~label = function
   | Resource.Dir dir -> dir
   | r -> Fmt.invalid_arg "get_dir(%s): %a" label Resource.pp r
@@ -182,61 +244,41 @@ let reset_file ~truncate ~append r =
       r := File { f with contents; stat; pos }
   | _ -> ()
 
-let std_table =
-  let open Resource in
-  Fd_table.add (Fd.of_int 0) (ref Stdin) Fd_table.empty
-  |> Fd_table.add (Fd.of_int 1) (ref Stdout)
-  |> Fd_table.add (Fd.of_int 2) (ref Stderr)
-
-let fd_table : resource ref Fd_table.t ref = ref std_table
-
-let update_fd_table_with_result fn =
-  let v, new_fd_table = fn !fd_table in
-  fd_table := new_fd_table;
-  v
-
-let update_fd_table fn =
-  let () = update_fd_table_with_result (fun fd -> ((), fn fd)) in
-  ()
-
 let update_entry ?(if_missing = fun () -> ()) fd fds fn =
-  match Fd_table.find_opt fd fds with None -> if_missing () | Some e -> fn e
+  match Fd_tbl.find_opt fd fds with None -> if_missing () | Some e -> fn e
 
 let read_fd_table fn = fn !fd_table
 
-let next_fd_from_fds fds =
-  Fd_table.to_list fds
-  |> List.sort (fun (i, _) (j, _) -> Fd.compare i j)
-  |> List.rev |> List.hd |> fst |> Fd.incr
+let next_fd_from_fds ~sw fds =
+  Fd_tbl.to_list fds
+  |> List.sort (fun (i, _) (j, _) -> Int.compare i j)
+  |> List.rev |> List.hd |> fst
+  |> fun i -> Fd.of_int ~sw (i + 1)
 
-let next_fd () = read_fd_table next_fd_from_fds
+let next_fd sw = read_fd_table (next_fd_from_fds ~sw)
 
-let dup fd =
-  let r = read_fd_table (Fd_table.find_opt fd) in
+let dup ~sw fd =
+  let r = read_fd_table (Fd_tbl.find_opt fd) in
   match r with
   | None -> Error.badf ()
   | Some r ->
-      let new_fd = next_fd () in
-      let () = update_fd_table @@ fun tbl -> Fd_table.add new_fd r tbl in
+      let new_fd = next_fd sw in
+      let () = update_fd_table @@ fun tbl -> Fd_tbl.add new_fd r tbl in
       new_fd
 
-let close fd =
-  update_fd_table @@ fun fds ->
-  match Fd_table.find_opt fd fds with
-  | None -> Error.badf ~msg:"close" ()
-  | Some _ -> Fd_table.remove fd fds
+let close fd = Fd.close fd
 
 let dup2 ~src ~tgt =
-  let src_r = read_fd_table (Fd_table.find_opt src) in
-  let tgt_r = read_fd_table (Fd_table.find_opt tgt) in
+  let src_r = read_fd_table (Fd_tbl.find_opt src) in
+  let tgt_r = read_fd_table (Fd_tbl.find_opt tgt) in
   match src_r with
   | None -> Error.badf ()
   | Some r -> (
       match tgt_r with
-      | None -> update_fd_table @@ fun tbl -> Fd_table.add tgt r tbl
+      | None -> update_fd_table @@ fun tbl -> Fd_tbl.add tgt r tbl
       | Some _ ->
           close tgt;
-          update_fd_table @@ fun tbl -> Fd_table.add tgt r tbl)
+          update_fd_table @@ fun tbl -> Fd_tbl.add tgt r tbl)
 
 let default_stat =
   Eio.File.Stat.
@@ -418,7 +460,7 @@ module Filesystem = struct
           if is_confined ~root:cwd_path resource_path then r
           else Error.permission_denied resource_path
       | Dir.Dir_fd dir ->
-          let dir = read_fd_table (Fd_table.find dir) in
+          let dir = read_fd_table (Fd_tbl.find' dir) in
           let resource_path, r =
             find_entry_relative_to_dir ~check:true ~follow fs dir path
           in
@@ -432,7 +474,7 @@ module Filesystem = struct
 end
 
 let find_by_inode inode fds =
-  Fd_table.to_list fds
+  Fd_tbl.to_list fds
   |> List.find_opt (fun (_, v) ->
       match v with
       | Resource.File f -> f.stat.ino = inode
@@ -443,6 +485,16 @@ let entries = function
   | Resource.Dir { Dir.entries; _ } -> entries
   | r -> Fmt.invalid_arg "entries: %a" Resource.pp r
 
+let pipe sw =
+  let q = Pipe.make () in
+  let r = ref (Resource.Pipe q) in
+  let rfd = next_fd sw in
+  let () = update_fd_table @@ Fd_tbl.add rfd r in
+  let wfd = next_fd sw in
+  update_fd_table_with_result @@ fun tbl ->
+  let tbl = Fd_tbl.add wfd r tbl in
+  ((rfd, wfd), tbl)
+
 let openat ~mode:_ ~sw dir_fd path flags =
   let path = check_path path in
   let is_create = Open_flags.(mem o_creat flags) in
@@ -454,10 +506,10 @@ let openat ~mode:_ ~sw dir_fd path flags =
   match is_create || is_excl with
   | false ->
       update_fd_table_with_result @@ fun fds ->
-      let fd = next_fd_from_fds fds in
       let r = Filesystem.lookup ~follow dir_fd path in
       reset_file ~truncate ~append r;
-      (fd, Fd_table.add fd r fds)
+      let fd = next_fd_from_fds fds ~sw in
+      (fd, Fd_tbl.add fd r fds)
   | true -> (
       let () =
         try
@@ -467,16 +519,15 @@ let openat ~mode:_ ~sw dir_fd path flags =
         with Eio.Exn.Io (Eio.Fs.(E (Not_found _)), _) -> ()
       in
       update_fd_table_with_result @@ fun fds ->
-      let fd = next_fd_from_fds fds in
       let r =
         try Option.some @@ Filesystem.lookup ~follow dir_fd path
         with Eio.Exn.Io (Eio.Fs.(E (Not_found _)), _) -> None
       in
       match r with
       | Some r ->
-          let fds = Fd_table.add fd r fds in
+          let fd = next_fd_from_fds fds ~sw in
+          let fds = Fd_tbl.add fd r fds in
           reset_file ~truncate ~append r;
-          Eio.Switch.on_release sw (fun () -> close fd);
           (fd, fds)
       | None ->
           let fname = Filename.basename path in
@@ -495,8 +546,8 @@ let openat ~mode:_ ~sw dir_fd path flags =
           rdir := Resource.Dir dir;
           let new_file = ref (Resource.File f) in
           Filesystem.add_file f.stat.ino new_file;
-          let fds = Fd_table.add fd new_file fds in
-          Eio.Switch.on_release sw (fun () -> close fd);
+          let fd = next_fd_from_fds fds ~sw in
+          let fds = Fd_tbl.add fd new_file fds in
           (fd, fds))
 
 let statat ~follow dir_fd path =
@@ -631,7 +682,7 @@ let rename dir_fd old_path new_dir new_path =
 
 let stat fd =
   read_fd_table @@ fun fds ->
-  match Fd_table.find_opt fd fds |> Option.map ( ! ) with
+  match Fd_tbl.find_opt fd fds |> Option.map ( ! ) with
   | None -> Error.badf ()
   | Some (File f) -> f.stat
   | Some (Dir dir) -> dir.stat
@@ -661,6 +712,7 @@ let writev fd bufs =
   let () =
     update_entry fd fds @@ fun r ->
     match !r with
+    | Pipe p -> List.iter (Pipe.write p) bufs
     | File e ->
         let size = e.stat.size in
         (* If the position is equal to the size then we just append. *)
@@ -690,12 +742,30 @@ let writev fd bufs =
   in
   (Cstruct.length (Cstruct.concat bufs), fds)
 
+let blit_into_bufs buf bufs =
+  let i = ref 0 in
+  let len = Cstruct.length buf in
+  List.iter
+    (fun obuf ->
+      if !i >= len then ()
+      else
+        let olen = Cstruct.length obuf in
+        let actual_len = min (len - !i) olen in
+        Cstruct.blit buf !i obuf 0 actual_len;
+        i := !i + actual_len)
+    bufs;
+  !i
+
 let readv fd bufs =
   update_fd_table_with_result @@ fun fds ->
   let read = ref 0 in
   let () =
     update_entry fd fds @@ fun r ->
     match !r with
+    | Pipe p -> (
+        match Pipe.read p with
+        | Some buf -> read := blit_into_bufs buf bufs
+        | None -> raise End_of_file)
     | File e ->
         let pos = ref e.pos in
         let size = Optint.Int63.to_int e.stat.size in
diff --git a/test/fs.md b/test/fs.md
index cf78672..452fc50 100644
--- a/test/fs.md
+++ b/test/fs.md
@@ -383,12 +383,15 @@ Confined:
 
 # Low level API
 
+Using `dup` to create a new file descriptor.
+
 ```ocaml
 # run ~clear:[ "hello.txt"; "world.txt" ] @@ fun env ->
   let () =
+    Eio.Switch.run @@ fun sw ->
     Eio.Path.with_open_out ~create:(`If_missing 0o644) (env#fs / "hello.txt") @@ fun flow ->
     let fd = Eio_mem.Resource.fd_opt flow |> Option.get in
-    let nfd = L.dup fd in
+    let nfd = L.dup ~sw fd in
     let _ : int = L.writev nfd [ Cstruct.of_string "Hello, World" ] in
     ()
   in
@@ -396,3 +399,17 @@ Confined:
 +Got: Hello, World
 - : unit = ()
 ```
+
+Using `pipe` to create a read/write pipe.
+
+```ocaml
+# run ~clear:[ "hello.txt"; "world.txt" ] @@ fun _ ->
+  Eio.Switch.run @@ fun sw ->
+  let r, w = L.pipe sw in
+  let _ : int = L.writev w [ Cstruct.of_string "Hello, world!" ] in
+  L.close w;
+  Eio.traceln "Got: %s" (Eio.Flow.read_all (Eio_mem.Flow.of_fd r));;
++Got: Hello, world!
+- : unit = ()
+```
+