diff --git a/src/render.rs b/src/render.rs
index 220b552..9f2573c 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -1,7 +1,6 @@
 use crate::geom::{Index, Meters, Vec2, Vec3, Vec3u};
-use crate::mat;
 use crate::real::ToFloat as _;
-use crate::sim::{Cell, GenericSim, StaticSim};
+use crate::sim::{GenericSim, Sample, StaticSim};
 use crate::meas::AbstractMeasurement;
 use crossterm::{cursor, QueueableCommand as _};
 use crossterm::style::{style, Color, PrintStyledContent};
@@ -188,7 +187,7 @@ impl<'a, S: GenericSim> RenderSteps<'a, S> {
         }
     }
 
-    fn get_at_px(&self, x_px: u32, y_px: u32) -> Cell {
+    fn get_at_px(&self, x_px: u32, y_px: u32) -> Sample {
         let x_prop = x_px as f32 / self.im.width() as f32;
         let x_m = x_prop * (self.sim.width() as f32 * self.sim.feature_size() as f32);
         let y_prop = y_px as f32 / self.im.height() as f32;
@@ -231,7 +230,7 @@ impl<'a, S: GenericSim> RenderSteps<'a, S> {
         self.render_vector_field(Rgb([0xff, 0xff, 0xff]), 1.0e5 * scale, |cell| cell.m().xy().to_f32());
     }
 
-    fn render_vector_field<F: Fn(&Cell<mat::Static>) -> Vec2<f32>>(&mut self, color: Rgb<u8>, typical: f32, measure: F) {
+    fn render_vector_field<F: Fn(&Sample) -> Vec2<f32>>(&mut self, color: Rgb<u8>, typical: f32, measure: F) {
         let w = self.im.width();
         let h = self.im.height();
         let vec_spacing = 10;
@@ -246,7 +245,7 @@ impl<'a, S: GenericSim> RenderSteps<'a, S> {
             }
         }
     }
-    fn render_scalar_field<F: Fn(&Cell<mat::Static>) -> f32 + Sync>(&mut self, typical: f32, signed: bool, slot: u32, measure: F) {
+    fn render_scalar_field<F: Fn(&Sample) -> f32 + Sync>(&mut self, typical: f32, signed: bool, slot: u32, measure: F) {
         // XXX: get_at_px borrows self, so we need to clone the image to operate on it mutably.
         let mut im = self.im.clone();
         let w = im.width();
@@ -292,7 +291,7 @@ impl<'a, S: GenericSim> RenderSteps<'a, S> {
         }
     }
 
-    fn field_vector<F: Fn(&Cell<mat::Static>) -> Vec2<f32>>(&self, xidx: u32, yidx: u32, size: u32, measure: &F) -> Vec2<f32> {
+    fn field_vector<F: Fn(&Sample) -> Vec2<f32>>(&self, xidx: u32, yidx: u32, size: u32, measure: &F) -> Vec2<f32> {
         let mut field = Vec2::default();
         let w = self.im.width();
         let h = self.im.height();
diff --git a/src/sim.rs b/src/sim.rs
index db897ba..670cb8b 100644
--- a/src/sim.rs
+++ b/src/sim.rs
@@ -196,7 +196,7 @@ impl<'a> From<StepParametersMut<'a>> for StepParameters<'a> {
 }
 
 pub trait GenericSim: Send + Sync + DynClone {
-    fn sample(&self, pos: Meters) -> Cell<mat::Static>;
+    fn sample(&self, pos: Meters) -> Sample;
     fn impulse_e_meters(&mut self, pos: Meters, amount: Vec3);
     fn impulse_h_meters(&mut self, pos: Meters, amount: Vec3);
     fn impulse_b_meters(&mut self, pos: Meters, amount: Vec3);
@@ -240,7 +240,10 @@ pub trait GenericSim: Send + Sync + DynClone {
                 let cell = self.sample(idx.to_meters(self.feature_size()));
                 *e = cell.e();
                 *h = cell.h();
-                cell.mat
+                mat::Static {
+                    conductivity: cell.conductivity(),
+                    m: cell.m(),
+                }
             });
         state
     }
@@ -248,13 +251,13 @@ pub trait GenericSim: Send + Sync + DynClone {
 dyn_clone::clone_trait_object!(GenericSim);
 
 impl<'a> dyn GenericSim + 'a {
-    pub fn get<C: Coord>(&self, at: C) -> Cell<mat::Static> {
+    pub fn get<C: Coord>(&self, at: C) -> Sample {
         self.sample(at.to_meters(self.feature_size()))
     }
     /// Apply `F` to each Cell, and sum the results.
     pub fn map_sum<F, Ret>(&self, f: F) -> Ret
     where
-          F: Fn(&Cell<mat::Static>) -> Ret + Sync,
+          F: Fn(&Sample) -> Ret + Sync,
           Ret: Sum<Ret> + Send,
     {
         self.map_sum_enumerated(|_at: Index, cell| f(cell))
@@ -262,7 +265,7 @@ impl<'a> dyn GenericSim + 'a {
 
     pub fn map_sum_enumerated<C, F, Ret>(&self, f: F) -> Ret
     where C: Coord,
-          F: Fn(C, &Cell<mat::Static>) -> Ret + Sync,
+          F: Fn(C, &Sample) -> Ret + Sync,
           Ret: Sum<Ret> + Send,
     {
         let (w, h, d) = (self.width(), self.height(), self.depth());
@@ -283,7 +286,7 @@ impl<'a> dyn GenericSim + 'a {
     /// Apply `F` to each Cell, and sum the results.
     pub fn map_sum_over<F, Ret, Reg>(&self, region: &Reg, f: F) -> Ret
     where
-          F: Fn(&Cell<mat::Static>) -> Ret + Sync,
+          F: Fn(&Sample) -> Ret + Sync,
           Ret: Sum<Ret> + Default + Send,
           Reg: Region + ?Sized
     {
@@ -292,7 +295,7 @@ impl<'a> dyn GenericSim + 'a {
 
     pub fn map_sum_over_enumerated<C, F, Ret, Reg>(&self, region: &Reg, f: F) -> Ret
     where C: Coord,
-          F: Fn(C, &Cell<mat::Static>) -> Ret + Sync,
+          F: Fn(C, &Sample) -> Ret + Sync,
           Ret: Sum<Ret> + Default + Send,
           Reg: Region + ?Sized,
     {
@@ -541,17 +544,18 @@ impl<M: Material> SimState<M> {
 }
 
 impl<M: Material + Clone + Send + Sync + 'static> GenericSim for SimState<M> {
-    fn sample(&self, pos: Meters) -> Cell<mat::Static> {
+    fn sample(&self, pos: Meters) -> Sample {
         // TODO: smarter sampling than nearest neighbor?
         let pos_sim = pos.to_index(self.feature_size());
         let idx = [pos_sim.z() as usize, pos_sim.y() as _, pos_sim.x() as _];
         match self.cells.get(idx) {
-            Some(mat) => Cell {
+            Some(mat) => Sample {
                 state: CellState {
                     e: self.e[idx],
                     h: self.h[idx],
                 },
-                mat: mat::Static::from_material(mat),
+                m: mat.m(),
+                conductivity: mat.step_parameters().conductivity(),
             },
             None => Default::default(),
         }
@@ -697,9 +701,10 @@ impl<M> SimState<M> {
 ///           +------------+------------+
 ///
 #[derive(Clone, Default, Serialize, Deserialize)]
-pub struct Cell<M = mat::Static> {
+pub struct Sample {
     state: CellState,
-    mat: M,
+    m: Vec3,
+    conductivity: Vec3,
 }
 
 struct Neighbors<'a> {
@@ -726,7 +731,7 @@ impl<'a> Neighbors<'a> {
     }
 }
 
-impl<M> Cell<M> {
+impl Sample {
     pub fn e(&self) -> Vec3 {
         self.state.e()
     }
@@ -752,9 +757,7 @@ impl<M> Cell<M> {
     pub fn hz(&self) -> Flt {
         Flt::from_primitive(self.h().z())
     }
-}
 
-impl<M: Material> Cell<M> {
     pub fn b(&self) -> Vec3 {
         (self.h() + self.m()) * consts::real::MU0()
     }
@@ -769,10 +772,10 @@ impl<M: Material> Cell<M> {
     }
 
     pub fn m(&self) -> Vec3 {
-        self.mat.m()
+        self.m
     }
     pub fn conductivity(&self) -> Vec3 {
-        self.mat.conductivity()
+        self.conductivity
     }
 
     pub fn current_density(&self) -> Vec3 {