diff --git a/Cargo.toml b/Cargo.toml
index 6fefd67..9a0174b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "aerosol"
-version = "1.0.0-alpha.4"
+version = "1.0.0-alpha.5"
 authors = ["Diggory Blake <diggsey@googlemail.com>"]
 edition = "2018"
 description = "Simple dependency injection for Rust"
@@ -23,6 +23,7 @@ axum = { version = "0.6", optional = true }
 tracing = { version = "0.1", optional = true }
 thiserror = { version = "1.0", optional = true }
 anyhow = { version = "1.0" }
+frunk = "0.4.2"
 
 [dev-dependencies]
 tokio = { version = "1.0", features = ["macros"] }
diff --git a/src/async_.rs b/src/async_.rs
index 4520955..58911f7 100644
--- a/src/async_.rs
+++ b/src/async_.rs
@@ -5,20 +5,18 @@ use std::{
     task::{Context, Poll},
 };
 
-use crate::{
-    resource::{unwrap_resource, Resource},
-    slot::SlotDesc,
-    state::Aerosol,
-};
+use frunk::prelude::HList;
+
+use crate::{resource::Resource, slot::SlotDesc, state::Aerosol};
 
-pub(crate) struct WaitForSlot<T: Resource> {
-    state: Aerosol,
+pub(crate) struct WaitForSlot<R: HList, T: Resource> {
+    state: Aerosol<R>,
     wait_index: Option<usize>,
     insert_placeholder: bool,
     phantom: PhantomData<fn() -> T>,
 }
 
-impl<T: Resource> Future for WaitForSlot<T> {
+impl<R: HList, T: Resource> Future for WaitForSlot<R, T> {
     type Output = Option<T>;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
@@ -28,11 +26,11 @@ impl<T: Resource> Future for WaitForSlot<T> {
     }
 }
 
-impl Aerosol {
+impl<R: HList> Aerosol<R> {
     pub(crate) fn wait_for_slot_async<T: Resource>(
         &self,
         insert_placeholder: bool,
-    ) -> WaitForSlot<T> {
+    ) -> WaitForSlot<R, T> {
         WaitForSlot {
             state: self.clone(),
             wait_index: None,
@@ -48,30 +46,12 @@ impl Aerosol {
             SlotDesc::Placeholder => self.wait_for_slot_async::<T>(false).await,
         }
     }
-    /// Get an instance of `T` from the AppState, and panic if not found.
-    /// This function does not attempt to construct `T` if it does not exist.
-    pub async fn get_async<T: Resource>(&self) -> T {
-        unwrap_resource(self.try_get_async().await)
-    }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    #[tokio::test]
-    async fn get_with() {
-        let state = Aerosol::new().with(42);
-        assert_eq!(state.get_async::<i32>().await, 42);
-    }
-
-    #[tokio::test]
-    async fn get_inserted() {
-        let state = Aerosol::new();
-        state.insert(42);
-        assert_eq!(state.get_async::<i32>().await, 42);
-    }
-
     #[tokio::test]
     async fn try_get_some() {
         let state = Aerosol::new().with(42);
diff --git a/src/async_constructible.rs b/src/async_constructible.rs
index 73dae72..e9ed033 100644
--- a/src/async_constructible.rs
+++ b/src/async_constructible.rs
@@ -1,6 +1,7 @@
 use std::{any::Any, sync::Arc};
 
 use async_trait::async_trait;
+use frunk::prelude::HList;
 
 use crate::{
     resource::{unwrap_constructed, Resource},
@@ -111,14 +112,14 @@ impl_async_constructible! {
 pub trait AsyncConstructibleResource: Resource + IndirectlyAsyncConstructible {}
 impl<T: Resource + IndirectlyAsyncConstructible> AsyncConstructibleResource for T {}
 
-impl Aerosol {
+impl<R: HList> Aerosol<R> {
     /// Try to get or construct an instance of `T` asynchronously. Requires feature `async`.
     pub async fn try_obtain_async<T: AsyncConstructibleResource>(&self) -> Result<T, T::Error> {
         match self.try_get_slot() {
             Some(SlotDesc::Filled(x)) => Ok(x),
             Some(SlotDesc::Placeholder) | None => match self.wait_for_slot_async::<T>(true).await {
                 Some(x) => Ok(x),
-                None => match T::construct_async(self).await {
+                None => match T::construct_async(self.as_ref()).await {
                     Ok(x) => {
                         self.fill_placeholder::<T>(x.clone());
                         Ok(x)
@@ -139,7 +140,7 @@ impl Aerosol {
     pub async fn try_init_async<T: AsyncConstructibleResource>(&self) -> Result<(), T::Error> {
         match self.wait_for_slot_async::<T>(true).await {
             Some(_) => Ok(()),
-            None => match T::construct_async(self).await {
+            None => match T::construct_async(self.as_ref()).await {
                 Ok(x) => {
                     self.fill_placeholder::<T>(x);
                     Ok(())
@@ -340,6 +341,6 @@ mod tests {
     async fn obtain_impl() {
         let state = Aerosol::new();
         state.init_async::<Arc<DummyImpl>>().await;
-        state.get_async::<Arc<dyn DummyTrait>>().await;
+        state.try_get_async::<Arc<dyn DummyTrait>>().await.unwrap();
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index dc20923..9214ccf 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,6 +13,7 @@
 //!
 //! Provides integrations with the `axum` web framework. See the `axum` module
 //! for more information.
+pub use frunk;
 
 #[cfg(feature = "async")]
 mod async_;
@@ -20,6 +21,7 @@ mod async_;
 mod async_constructible;
 #[cfg(feature = "axum")]
 pub mod axum;
+mod macros;
 mod resource;
 mod slot;
 mod state;
diff --git a/src/macros.rs b/src/macros.rs
new file mode 100644
index 0000000..590265b
--- /dev/null
+++ b/src/macros.rs
@@ -0,0 +1,7 @@
+/// Define a custom `Aerosol` alias with a specific set of required types
+#[macro_export]
+macro_rules! Aero {
+    ($($tok:tt)*) => {
+        $crate::Aerosol<$crate::frunk::HList![$($tok)*]>
+    };
+}
diff --git a/src/main.rs b/src/main.rs
deleted file mode 100644
index f328e4d..0000000
--- a/src/main.rs
+++ /dev/null
@@ -1 +0,0 @@
-fn main() {}
diff --git a/src/state.rs b/src/state.rs
index 58fb0e6..256396c 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -1,6 +1,11 @@
-use std::{any::Any, sync::Arc, task::Poll};
+use std::{any::Any, marker::PhantomData, sync::Arc, task::Poll};
 
 use anymap::hashbrown::{Entry, Map};
+use frunk::{
+    hlist::{HFoldRightable, Sculptor},
+    prelude::HList,
+    HCons, HNil, Poly,
+};
 use parking_lot::RwLock;
 
 use crate::{
@@ -16,16 +21,67 @@ struct InnerAerosol {
 /// Stores a collection of resources keyed on resource type.
 /// Provides methods for accessing this collection.
 /// Can be cheaply cloned.
-#[derive(Debug, Clone, Default)]
-pub struct Aerosol {
+#[derive(Debug)]
+#[repr(transparent)]
+pub struct Aerosol<R: HList = HNil> {
     inner: Arc<RwLock<InnerAerosol>>,
+    phantom: PhantomData<Arc<R>>,
 }
 
 impl Aerosol {
     /// Construct a new instance of the type with no initial resources.
     pub fn new() -> Self {
-        Self::default()
+        Self {
+            inner: Default::default(),
+            phantom: PhantomData,
+        }
+    }
+}
+
+impl<R: HList> Clone for Aerosol<R> {
+    fn clone(&self) -> Self {
+        Self {
+            inner: self.inner.clone(),
+            phantom: PhantomData,
+        }
+    }
+}
+
+struct AerosolBuilderFolder;
+impl<R: HList, T: Resource> frunk::Func<(Aerosol<R>, T)> for AerosolBuilderFolder {
+    type Output = Aerosol<HCons<T, R>>;
+    fn call((aero, value): (Aerosol<R>, T)) -> Self::Output {
+        aero.with(value)
+    }
+}
+
+#[doc(hidden)]
+pub trait HTestable {
+    fn test<R: HList>(aero: &Aerosol<R>) -> bool;
+}
+
+impl HTestable for HNil {
+    fn test<R: HList>(_aero: &Aerosol<R>) -> bool {
+        true
+    }
+}
+
+impl<H: Resource, T: HTestable> HTestable for HCons<H, T> {
+    fn test<R: HList>(aero: &Aerosol<R>) -> bool {
+        aero.has::<H>() && T::test(aero)
+    }
+}
+
+impl<
+        R: Default + HFoldRightable<Poly<AerosolBuilderFolder>, Aerosol, Output = Aerosol<R>> + HList,
+    > Default for Aerosol<R>
+{
+    fn default() -> Self {
+        R::default().foldr(Poly(AerosolBuilderFolder), Aerosol::new())
     }
+}
+
+impl<R: HList> Aerosol<R> {
     /// Directly insert a resource into the collection. Panics if a resource of the
     /// same type already exists.
     pub fn insert<T: Resource>(&self, value: T) {
@@ -38,10 +94,76 @@ impl Aerosol {
     }
 
     /// Builder method equivalent to calling `insert()` but can be chained.
-    pub fn with<T: Resource>(self, value: T) -> Self {
+    pub fn with<T: Resource>(self, value: T) -> Aerosol<HCons<T, R>> {
         self.insert(value);
-        self
+        Aerosol {
+            inner: self.inner,
+            phantom: PhantomData,
+        }
+    }
+
+    /// Convert into a different variant of the Aerosol type. The new variant must
+    /// not require any resources which are not required as part of this type.
+    pub fn into<R2: HList, I>(self) -> Aerosol<R2>
+    where
+        R: Sculptor<R2, I>,
+    {
+        Aerosol {
+            inner: self.inner,
+            phantom: PhantomData,
+        }
     }
+
+    /// Reborrow as a different variant of the Aerosol type. The new variant must
+    /// not require any resources which are not required as part of this type.
+    #[allow(clippy::should_implement_trait)]
+    pub fn as_ref<R2: HList, I>(&self) -> &Aerosol<R2>
+    where
+        R: Sculptor<R2, I>,
+    {
+        // Safety: all Aerosol variants are `#[repr(transparent)]` wrappers around
+        // the same concrete type.
+        unsafe { std::mem::transmute(self) }
+    }
+
+    /// Try to convert into a different variant of the Aerosol type. Returns the
+    /// original type if one or more of the required resources are not fully
+    /// constructed.
+    pub fn try_into<R2: HList + HTestable>(self) -> Result<Aerosol<R2>, Self> {
+        if R2::test(&self) {
+            Ok(Aerosol {
+                inner: self.inner,
+                phantom: PhantomData,
+            })
+        } else {
+            Err(self)
+        }
+    }
+
+    /// Try to convert into a different variant of the Aerosol type. Returns
+    /// `None` if one or more of the required resources are not fully
+    /// constructed.
+    pub fn try_as_ref<R2: HList + HTestable>(&self) -> Option<&Aerosol<R2>> {
+        if R2::test(self) {
+            Some(
+                // Safety: all Aerosol variants are `#[repr(transparent)]` wrappers around
+                // the same concrete type.
+                unsafe { std::mem::transmute(self) },
+            )
+        } else {
+            None
+        }
+    }
+
+    /// Check if a resource with a specific type is fully constructed in this
+    /// aerosol instance
+    pub fn has<T: Resource>(&self) -> bool {
+        matches!(
+            self.inner.read().items.get::<Slot<T>>(),
+            Some(Slot::Filled(_))
+        )
+    }
+
     pub(crate) fn try_get_slot<T: Resource>(&self) -> Option<SlotDesc<T>> {
         self.inner.read().items.get().map(Slot::desc)
     }
@@ -89,8 +211,22 @@ impl Aerosol {
     }
 }
 
+impl<R: HList> AsRef<Aerosol> for Aerosol<R> {
+    fn as_ref(&self) -> &Aerosol {
+        Aerosol::as_ref(self)
+    }
+}
+
+impl<H, T: HList> From<Aerosol<HCons<H, T>>> for Aerosol {
+    fn from(value: Aerosol<HCons<H, T>>) -> Self {
+        value.into()
+    }
+}
+
 #[cfg(test)]
 mod tests {
+    use crate::Aero;
+
     use super::*;
 
     #[test]
@@ -105,4 +241,18 @@ mod tests {
         let state = Aerosol::new().with(13);
         state.insert(42);
     }
+
+    #[test]
+    fn default() {
+        let state: Aero![i32] = Aerosol::default();
+        state.insert("Hello, world!");
+    }
+
+    #[test]
+    fn convert() {
+        let state: Aero![i32, String, f32] = Aerosol::default();
+        state.insert("Hello, world!");
+        let state2: Aero![f32, String] = state.into();
+        let _state3: Aero![i32, String, f32] = state2.try_into().unwrap();
+    }
 }
diff --git a/src/sync.rs b/src/sync.rs
index bfaed41..4ed4b86 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -1,5 +1,7 @@
 use std::{task::Poll, thread};
 
+use frunk::{hlist::Plucker, prelude::HList};
+
 use crate::{
     resource::{unwrap_resource, Resource},
     slot::SlotDesc,
@@ -16,7 +18,7 @@ pub fn safe_park() {
     std::thread::park();
 }
 
-impl Aerosol {
+impl<R: HList> Aerosol<R> {
     /// Synchronously wait for the slot for `T` to not have a placeholder.
     /// Returns immediately if there is no `T` present, or if `T`'s slot is filled.
     pub(crate) fn wait_for_slot<T: Resource>(&self, insert_placeholder: bool) -> Option<T> {
@@ -37,9 +39,11 @@ impl Aerosol {
             SlotDesc::Placeholder => self.wait_for_slot::<T>(false),
         }
     }
-    /// Get an instance of `T` from the AppState, and panic if not found.
-    /// This function does not attempt to construct `T` if it does not exist.
-    pub fn get<T: Resource>(&self) -> T {
+    /// Get an instance of `T` from the AppState which is statically known to be present.
+    pub fn get<T: Resource, I>(&self) -> T
+    where
+        R: Plucker<T, I>,
+    {
         unwrap_resource(self.try_get())
     }
 }
@@ -51,14 +55,7 @@ mod tests {
     #[test]
     fn get_with() {
         let state = Aerosol::new().with(42);
-        assert_eq!(state.get::<i32>(), 42);
-    }
-
-    #[test]
-    fn get_inserted() {
-        let state = Aerosol::new();
-        state.insert(42);
-        assert_eq!(state.get::<i32>(), 42);
+        assert_eq!(state.get::<i32, _>(), 42);
     }
 
     #[test]
diff --git a/src/sync_constructible.rs b/src/sync_constructible.rs
index bffacfd..8572278 100644
--- a/src/sync_constructible.rs
+++ b/src/sync_constructible.rs
@@ -1,5 +1,7 @@
 use std::{any::Any, sync::Arc};
 
+use frunk::prelude::HList;
+
 use crate::{
     resource::{unwrap_constructed, Resource},
     slot::SlotDesc,
@@ -90,14 +92,14 @@ impl_constructible! {
 pub trait ConstructibleResource: Resource + IndirectlyConstructible {}
 impl<T: Resource + IndirectlyConstructible> ConstructibleResource for T {}
 
-impl Aerosol {
+impl<R: HList> Aerosol<R> {
     /// Try to get or construct an instance of `T`.
     pub fn try_obtain<T: ConstructibleResource>(&self) -> Result<T, T::Error> {
         match self.try_get_slot() {
             Some(SlotDesc::Filled(x)) => Ok(x),
             Some(SlotDesc::Placeholder) | None => match self.wait_for_slot::<T>(true) {
                 Some(x) => Ok(x),
-                None => match T::construct(self) {
+                None => match T::construct(self.as_ref()) {
                     Ok(x) => {
                         self.fill_placeholder::<T>(x.clone());
                         Ok(x)
@@ -118,7 +120,7 @@ impl Aerosol {
     pub fn try_init<T: ConstructibleResource>(&self) -> Result<(), T::Error> {
         match self.wait_for_slot::<T>(true) {
             Some(_) => Ok(()),
-            None => match T::construct(self) {
+            None => match T::construct(self.as_ref()) {
                 Ok(x) => {
                     self.fill_placeholder::<T>(x);
                     Ok(())
@@ -264,6 +266,6 @@ mod tests {
     fn obtain_impl() {
         let state = Aerosol::new();
         state.init::<Arc<DummyImpl>>();
-        state.get::<Arc<dyn DummyTrait>>();
+        state.try_get::<Arc<dyn DummyTrait>>().unwrap();
     }
 }