diff --git a/crates/applications/buffer_proto5/src/main.rs b/crates/applications/buffer_proto5/src/main.rs
index 15da818..cd53344 100644
--- a/crates/applications/buffer_proto5/src/main.rs
+++ b/crates/applications/buffer_proto5/src/main.rs
@@ -4,7 +4,7 @@
 
 use coremem::{Driver, mat, meas, SpirvDriver};
 use coremem::geom::{region, Cube, Dilate, Memoize, Meters, Region, Spiral, SwapYZ, Torus, Translate, Wrap};
-use coremem::mat::Ferroxcube3R1MH;
+use coremem::mat::{Ferroxcube3R1MH, IsoConductorOr};
 use coremem::real::{R32, Real as _};
 use coremem::render::CsvRenderer;
 use coremem::stim::{CurlStimulus, Exp1, Gated, Sinusoid1, TimeVarying as _};
@@ -14,7 +14,7 @@ use coremem::util::cache::DiskCache;
 use log::{error, info, warn};
 use serde::{Deserialize, Serialize};
 
-type Mat = spirv::IsoConductorOr<Ferroxcube3R1MH>;
+type Mat = IsoConductorOr<f32, Ferroxcube3R1MH>;
 
 #[allow(unused)]
 use coremem::geom::{Coord as _, Region as _};
diff --git a/crates/applications/multi_core_inverter/src/main.rs b/crates/applications/multi_core_inverter/src/main.rs
index f8a88ae..ec4da24 100644
--- a/crates/applications/multi_core_inverter/src/main.rs
+++ b/crates/applications/multi_core_inverter/src/main.rs
@@ -38,11 +38,11 @@
 
 use coremem::geom::{Meters, Torus};
 use coremem::sim::units::Seconds;
-use coremem::mat::{Ferroxcube3R1MH, IsomorphicConductor};
+use coremem::mat::{Ferroxcube3R1MH, IsoConductorOr, IsomorphicConductor};
 use coremem::spirv;
 use coremem::{Driver, SpirvDriver};
 
-type Mat = spirv::IsoConductorOr<Ferroxcube3R1MH>;
+type Mat = IsoConductorOr<f32, Ferroxcube3R1MH>;
 
 fn main() {
     coremem::init_logging();
diff --git a/crates/coremem/benches/driver.rs b/crates/coremem/benches/driver.rs
index 79c64c5..49f81e0 100644
--- a/crates/coremem/benches/driver.rs
+++ b/crates/coremem/benches/driver.rs
@@ -1,6 +1,6 @@
 use coremem::{Driver, SimState, SpirvDriver};
 use coremem::geom::Index;
-use coremem::mat::{Ferroxcube3R1MH, GenericMaterial, GenericMaterialNoPml, GenericMaterialOneField};
+use coremem::mat::{Ferroxcube3R1MH, IsoConductorOr, GenericMaterial, GenericMaterialNoPml, GenericMaterialOneField};
 use coremem::real::R32;
 use coremem::sim::spirv::{self, SpirvSim};
 use criterion::{BenchmarkId, criterion_group, criterion_main, Criterion};
@@ -28,7 +28,7 @@ pub fn bench_step_spirv(c: &mut Criterion) {
 }
 
 pub fn bench_step_spirv_iso_3r1(c: &mut Criterion) {
-    type Mat = spirv::IsoConductorOr<Ferroxcube3R1MH>;
+    type Mat = IsoConductorOr<f32, Ferroxcube3R1MH>;
     for size in &[10, 20, 40, 80, 160] {
         let sim: SpirvSim<Mat> = SpirvSim::new(Index::new(*size, *size, *size), 1e-5);
         c.bench_with_input(BenchmarkId::new("Driver::spirv_ISO3R1", size), &sim, |b, sim| {
diff --git a/crates/coremem/src/mat/linear.rs b/crates/coremem/src/mat/linear.rs
index 9550e2b..cd74be9 100644
--- a/crates/coremem/src/mat/linear.rs
+++ b/crates/coremem/src/mat/linear.rs
@@ -2,58 +2,9 @@ use crate::CellState;
 use crate::geom::Vec3;
 use crate::mat::Material;
 use crate::real::Real;
-use crate::sim::StepParametersMut;
 
 use serde::{Serialize, Deserialize};
 
-/// Material which has a conductivity parameter, but cannot be magnetized
-#[derive(Copy, Clone, Default, PartialEq, Serialize, Deserialize)]
-pub struct Conductor<V> {
-    pub conductivity: V,
-}
-
-pub type IsomorphicConductor<R> = Conductor<(R,)>;
-pub type AnisomorphicConductor<R> = Conductor<Vec3<R>>;
-
-impl<V> IsomorphicConductor<V> {
-    pub fn new(conductivity: V) -> Self {
-        Self {
-            conductivity: (conductivity,)
-        }
-    }
-}
-impl<V: Clone> IsomorphicConductor<V> {
-    pub fn iso_conductivity(&self) -> V {
-        self.conductivity.0.clone()
-    }
-}
-
-impl<R> AnisomorphicConductor<R> {
-    pub fn new(conductivity: Vec3<R>) -> Self {
-        Self {
-            conductivity
-        }
-    }
-}
-
-impl<R: Real> Into<AnisomorphicConductor<R>> for IsomorphicConductor<R> {
-    fn into(self) -> AnisomorphicConductor<R> {
-        AnisomorphicConductor::new(Vec3::uniform(self.conductivity.0))
-    }
-}
-
-impl<R: Real> Material<R> for AnisomorphicConductor<R> {
-    fn step_parameters_mut<'a>(&'a mut self) -> StepParametersMut<'a, R> {
-        StepParametersMut::default().with_conductivity(self.conductivity)
-    }
-}
-
-impl<R: Real> Material<R> for IsomorphicConductor<R> {
-    fn step_parameters_mut<'a>(&'a mut self) -> StepParametersMut<'a, R> {
-        StepParametersMut::default().with_conductivity(Vec3::uniform(self.conductivity.0))
-    }
-}
-
 /// Material which can be magnetized, but has no hysteresis and no coercivity.
 #[derive(Copy, Clone, Default, PartialEq, Serialize, Deserialize)]
 pub struct LinearMagnet<R> {
diff --git a/crates/coremem/src/mat/mod.rs b/crates/coremem/src/mat/mod.rs
index 7d3c900..c7f0baa 100644
--- a/crates/coremem/src/mat/mod.rs
+++ b/crates/coremem/src/mat/mod.rs
@@ -13,7 +13,7 @@ mod linear;
 
 pub use bh_ferromagnet::*;
 pub use mb_ferromagnet::*;
-pub use coremem_types::mat::{MHPgram, Ferroxcube3R1MH};
+pub use coremem_types::mat::{AnisomorphicConductor, Ferroxcube3R1MH, IsoConductorOr, IsomorphicConductor, MHPgram};
 pub use linear::*;
 
 #[enum_dispatch]
@@ -311,3 +311,17 @@ impl<R: Real> Material<R> for GenericMaterialOneField<R> {
         }
     }
 }
+
+// coremem_types adapters
+impl<R: Real> Material<R> for AnisomorphicConductor<R> {
+    fn step_parameters_mut<'a>(&'a mut self) -> StepParametersMut<'a, R> {
+        let c = coremem_types::mat::Material::conductivity(self);
+        StepParametersMut::default().with_conductivity(c)
+    }
+}
+impl<R: Real> Material<R> for IsomorphicConductor<R> {
+    fn step_parameters_mut<'a>(&'a mut self) -> StepParametersMut<'a, R> {
+        let c = coremem_types::mat::Material::conductivity(self);
+        StepParametersMut::default().with_conductivity(c)
+    }
+}
diff --git a/crates/coremem/src/sim/spirv/bindings.rs b/crates/coremem/src/sim/spirv/bindings.rs
index 59b4a40..5fd671c 100644
--- a/crates/coremem/src/sim/spirv/bindings.rs
+++ b/crates/coremem/src/sim/spirv/bindings.rs
@@ -2,7 +2,7 @@ use serde::de::Deserializer;
 use serde::ser::Serializer;
 use serde::{Deserialize, Serialize};
 
-use crate::mat::{AnisomorphicConductor, IsomorphicConductor, Ferroxcube3R1MH, MaterialExt as _, MBFerromagnet, MBPgram, MHPgram, Static};
+use crate::mat::{AnisomorphicConductor, IsoConductorOr, IsomorphicConductor, Ferroxcube3R1MH, MaterialExt as _, MBFerromagnet, MBPgram, MHPgram, Static};
 use crate::geom::{Index, Vec3, Vec3u};
 
 /// hide the actual spirv backend structures inside a submodule to make their use/boundary clear.
@@ -10,7 +10,7 @@ mod ffi {
     pub use spirv_backend::entry_points;
     pub use spirv_backend::sim::SerializedSimMeta;
     pub use spirv_backend::support::Optional;
-    pub use spirv_backend::mat::{FullyGenericMaterial, IsoConductorOr};
+    pub use spirv_backend::mat::FullyGenericMaterial;
     pub use coremem_types::mat::MBPgram;
 }
 
@@ -88,6 +88,7 @@ impl IntoLib for ffi::MBPgram<f32> {
 
 identity!( => MHPgram<f32>);
 identity!( => Ferroxcube3R1MH);
+identity!(R, M, => IsoConductorOr<R, M>);
 
 #[derive(Clone, Default, PartialEq, Serialize, Deserialize)]
 pub struct FullyGenericMaterial {
@@ -170,52 +171,6 @@ impl From<Ferroxcube3R1MH> for FullyGenericMaterial {
     }
 }
 
-#[derive(Copy, Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
-pub struct IsoConductorOr<M> {
-    value: f32,
-    mat: M,
-}
-
-impl<L: IntoFfi> IntoFfi for IsoConductorOr<L> {
-    type Ffi = ffi::IsoConductorOr<L::Ffi>;
-    fn into_ffi(self) -> Self::Ffi {
-        Self::Ffi {
-            value: self.value,
-            mat: self.mat.into_ffi(),
-        }
-    }
-}
-
-impl<F: IntoLib> IntoLib for ffi::IsoConductorOr<F> {
-    type Lib = IsoConductorOr<F::Lib>;
-    fn into_lib(self) -> Self::Lib {
-        Self::Lib {
-            value: self.value,
-            mat: self.mat.into_lib(),
-        }
-    }
-}
-
-impl<M: Default> From<IsomorphicConductor<f32>> for IsoConductorOr<M> {
-    fn from(m: IsomorphicConductor<f32>) -> Self {
-        IsoConductorOr {
-            value: m.iso_conductivity(),
-            mat: Default::default(),
-        }
-    }
-}
-
-// XXX: can't do this for generic M, because that creates duplicate `From` impls for the
-// IsomorphicConductor itself
-impl From<Ferroxcube3R1MH> for IsoConductorOr<Ferroxcube3R1MH> {
-    fn from(mat: Ferroxcube3R1MH) -> Self {
-        IsoConductorOr {
-            value: -1.0,
-            mat,
-        }
-    }
-}
-
 // this is bitwise- and type-compatible with the spirv SimMeta, except we need serde traits
 #[derive(Clone, Default, Serialize, Deserialize)]
 pub struct SimMeta {
diff --git a/crates/coremem/src/sim/spirv/mod.rs b/crates/coremem/src/sim/spirv/mod.rs
index 526ae10..233947c 100644
--- a/crates/coremem/src/sim/spirv/mod.rs
+++ b/crates/coremem/src/sim/spirv/mod.rs
@@ -15,7 +15,7 @@ use crate::stim::AbstractStimulus;
 use coremem_types::mat::Material;
 
 mod bindings;
-pub use bindings::{entry_points, IntoFfi, IntoLib, IsoConductorOr, FullyGenericMaterial, Remote, SimMeta};
+pub use bindings::{entry_points, IntoFfi, IntoLib, FullyGenericMaterial, Remote, SimMeta};
 
 /// Wrapper around an inner state object which offloads stepping onto a spirv backend (e.g. GPU).
 #[derive(Clone, Default, Serialize, Deserialize)]
@@ -892,15 +892,16 @@ mod test {
                             rng.gen_range(0.0..1e6),
                             rng.gen_range(0.0..1e6),
                         );
-                        ref_state.put_material(Index::new(x, y, z), AnisomorphicConductor::new(cond.cast()));
-                        dut_state.put_material(Index::new(x, y, z), AnisomorphicConductor::new(cond.cast()));
+                        let m = AnisomorphicConductor::new(cond.cast());
+                        ref_state.put_material(Index::new(x, y, z), m);
+                        let m = AnisomorphicConductor::new(cond.cast());
+                        dut_state.put_material(Index::new(x, y, z), m);
                     }
                 }
             }
 
             ref_state.apply_stimulus(&RngStimulus::new(seed));
             dut_state.apply_stimulus(&RngStimulus::new(seed));
-
             test_same_explicit(ref_state, dut_state, steps);
         }
 
diff --git a/crates/spirv_backend/src/mat.rs b/crates/spirv_backend/src/mat.rs
index e2c319b..028ca6f 100644
--- a/crates/spirv_backend/src/mat.rs
+++ b/crates/spirv_backend/src/mat.rs
@@ -25,41 +25,5 @@ impl Material<f32> for FullyGenericMaterial {
     }
 }
 
-/// Optimized material aimed at saving space for the common case of a simulation that contains
-/// isomorphic conductors plus one exception material.
-#[derive(Copy, Clone, Default, PartialEq)]
-pub struct IsoConductorOr<M> {
-    /// conductivity, if >= 0, else ignored & used to signal the other material
-    pub value: f32,
-    pub mat: M,
-}
-
-impl<M: Default> IsoConductorOr<M> {
-    pub fn new_conductor(conductivity: f32) -> Self {
-        Self {
-            value: conductivity,
-            mat: Default::default(),
-        }
-    }
-    pub fn new_other() -> Self {
-        Self {
-            value: -1.0,
-            mat: Default::default()
-        }
-    }
-}
-
-impl<M: Material<f32> + Copy> Material<f32> for IsoConductorOr<M> {
-    fn conductivity(&self) -> Vec3<f32> {
-        Vec3::uniform(self.value.max(0.0))
-    }
-    fn move_b_vec(&self, m: Vec3<f32>, target_b: Vec3<f32>) -> Vec3<f32> {
-        if self.value < 0.0 {
-            let mat = self.mat;  //< XXX hack for ZST
-            mat.move_b_vec(m, target_b)
-        } else {
-            m
-        }
-    }
-}
+pub type IsoConductorOr<M> = coremem_types::mat::IsoConductorOr<f32, M>;
 
diff --git a/crates/types/src/mat/conductor.rs b/crates/types/src/mat/conductor.rs
index 76eb91d..039b8d3 100644
--- a/crates/types/src/mat/conductor.rs
+++ b/crates/types/src/mat/conductor.rs
@@ -1,4 +1,4 @@
-use crate::mat::Material;
+use crate::mat::{Discriminable, Material};
 use crate::real::Real;
 use crate::vec::Vec3;
 
@@ -10,7 +10,31 @@ use serde::{Serialize, Deserialize};
 #[derive(Copy, Clone, Default, PartialEq)]
 pub struct Conductor<T>(T);
 pub type AnisomorphicConductor<R> = Conductor<Vec3<R>>;
-pub type IsomorphicConductor<R> = Conductor<R>;
+pub type IsomorphicConductor<R> = Conductor<(R,)>;
+
+impl<R> IsomorphicConductor<R> {
+    pub fn new(c: R) -> Self {
+        Self((c,))
+    }
+}
+
+impl<V: Clone> IsomorphicConductor<V> {
+    pub fn iso_conductivity(&self) -> V {
+        self.0.0.clone()
+    }
+}
+
+impl<R> AnisomorphicConductor<R> {
+    pub fn new(c: Vec3<R>) -> Self {
+        Self(c)
+    }
+}
+
+impl<R: Real> Into<AnisomorphicConductor<R>> for IsomorphicConductor<R> {
+    fn into(self) -> AnisomorphicConductor<R> {
+        AnisomorphicConductor::new(Vec3::uniform(self.iso_conductivity()))
+    }
+}
 
 impl<R: Real> Material<R> for AnisomorphicConductor<R> {
     fn conductivity(&self) -> Vec3<R> {
@@ -20,7 +44,20 @@ impl<R: Real> Material<R> for AnisomorphicConductor<R> {
 
 impl<R: Real> Material<R> for IsomorphicConductor<R> {
     fn conductivity(&self) -> Vec3<R> {
-        Vec3::uniform(self.0)
+        Vec3::uniform(self.iso_conductivity())
     }
 }
 
+impl<R: Real> Discriminable for IsomorphicConductor<R> {
+    fn discr(&self) -> u32 {
+        let cond = self.iso_conductivity();
+        if cond < R::zero() {
+            (-cond.to_f32()) as u32
+        } else {
+            0
+        }
+    }
+    fn make_discr(d: u32) -> Self {
+        Self::new(R::from_primitive(-(d as i32)))
+    }
+}
diff --git a/crates/types/src/mat/mod.rs b/crates/types/src/mat/mod.rs
index 0cd233e..1b7c0ea 100644
--- a/crates/types/src/mat/mod.rs
+++ b/crates/types/src/mat/mod.rs
@@ -8,6 +8,10 @@ pub use conductor::{AnisomorphicConductor, IsomorphicConductor};
 pub use mb_pgram::MBPgram;
 pub use mh_pgram::{Ferroxcube3R1MH, MHPgram};
 
+#[cfg(feature = "serde")]
+use serde::{Serialize, Deserialize};
+
+
 pub trait Material<R: Real>: Sized {
     fn conductivity(&self) -> Vec3<R> {
         Default::default()
@@ -19,3 +23,144 @@ pub trait Material<R: Real>: Sized {
         m
     }
 }
+
+/// any type which may hold a discriminant internally.
+pub trait Discriminable {
+    fn discr(&self) -> u32;
+    fn make_discr(d: u32) -> Self;
+}
+
+pub struct D0<T>(pub T);
+pub struct D1<T>(pub T);
+
+#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
+#[cfg_attr(feature = "fmt", derive(Debug))]
+#[derive(Copy, Clone, Default, PartialEq)]
+pub struct DiscrMat2<M0, M1> {
+    m0: M0,
+    m1: M1,
+}
+
+impl<M0, M1> DiscrMat2<M0, M1> {
+    fn new_from_fields(m0: M0, m1: M1) -> Self {
+        Self { m0, m1 }
+    }
+}
+
+impl<M0: Discriminable, M1: Default> DiscrMat2<M0, M1> {
+    pub fn new0(m: M0) -> Self {
+        D0(m).into()
+    }
+    pub fn new1(m: M1) -> Self {
+        D1(m).into()
+    }
+}
+
+impl<M0: Discriminable, M1: Default> From<D0<M0>> for DiscrMat2<M0, M1> {
+    fn from(m0: D0<M0>) -> Self {
+        let m0 = m0.0;
+        assert!(m0.discr() == 0, "unexpected non-zero discriminant");
+        Self::new_from_fields(m0, Default::default())
+    }
+}
+
+impl<M0: Discriminable, M1> From<D1<M1>> for DiscrMat2<M0, M1> {
+    fn from(m1: D1<M1>) -> Self {
+        let m1 = m1.0;
+        Self::new_from_fields(M0::make_discr(1), m1)
+    }
+}
+
+impl<R: Real, M0: Discriminable + Material<R>, M1: Material<R> + Copy> Material<R> for DiscrMat2<M0, M1> {
+    fn conductivity(&self) -> Vec3<R> {
+        match self.m0.discr() {
+            0 => self.m0.conductivity(),
+            1 => {
+                let mat = self.m1;  //< XXX hack for ZST
+                mat.conductivity()
+            }
+            _ => panic!()
+            // _ => unreachable!(),
+        }
+    }
+    fn move_b_vec(&self, m: Vec3<R>, target_b: Vec3<R>) -> Vec3<R> {
+        match self.m0.discr() {
+            0 => self.m0.move_b_vec(m, target_b),
+            1 => {
+                let mat = self.m1;  //< XXX hack for ZST
+                mat.move_b_vec(m, target_b)
+            }
+            _ => panic!()
+            // _ => unreachable!(),
+        }
+    }
+}
+
+pub type IsoConductorOr<R, M1> = DiscrMat2<IsomorphicConductor<R>, M1>;
+
+impl<R: Real, M1: Default> IsoConductorOr<R, M1> {
+    pub fn new_conductor(conductivity: R) -> Self {
+        Self::new0(IsomorphicConductor::new(conductivity))
+    }
+    pub fn new_other(other: M1) -> Self {
+        Self::new1(other)
+    }
+}
+
+// XXX: can't do this for generic M, because that creates duplicate `From` impls for the
+// IsomorphicConductor itself
+impl<R: Real> From<Ferroxcube3R1MH> for IsoConductorOr<R, Ferroxcube3R1MH> {
+    fn from(mat: Ferroxcube3R1MH) -> Self {
+        IsoConductorOr::new1(mat)
+    }
+}
+impl<R: Real> From<IsomorphicConductor<R>> for IsoConductorOr<R, Ferroxcube3R1MH> {
+    fn from(mat: IsomorphicConductor<R>) -> Self {
+        IsoConductorOr::new0(mat)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::real::R32;
+
+    #[test]
+    fn iso_conductor_discr() {
+        type T = IsomorphicConductor<f32>;
+        let c = T::make_discr(5);
+        assert_eq!(c.discr(), 5);
+
+        let c = T::make_discr(0);
+        assert_eq!(c.discr(), 0);
+
+        let c = T::new(5.0);
+        assert_eq!(c.discr(), 0);
+
+        let c = T::new(0.0);
+        assert_eq!(c.discr(), 0);
+    }
+
+    #[test]
+    fn iso_conductor_or_3r1() {
+        let c: IsoConductorOr<f32, Ferroxcube3R1MH> = IsomorphicConductor::new(22.0f32).into();
+        assert!(c.conductivity() == Vec3::uniform(22.0f32));
+
+        let c: IsoConductorOr<f32, Ferroxcube3R1MH> = Ferroxcube3R1MH::new().into();
+        assert!(c.conductivity() == Vec3::zero());
+    }
+
+    #[test]
+    fn iso_conductor_or_aniso() {
+        type I = IsoConductorOr<R32, AnisomorphicConductor<R32>>;
+
+        let c = I::new0(IsomorphicConductor::new(22f32.cast()));
+        assert!(c.conductivity() == Vec3::uniform(22.0).cast());
+
+        let c = I::new1(AnisomorphicConductor::new(
+            Vec3::new(2.0, 3.0, 4.0).cast()
+        ));
+
+        assert!(c.conductivity() == Vec3::new(2.0, 3.0, 4.0).cast());
+    }
+}