diff --git a/src/MrGameEng.Simulation/AI/Suitability.cs b/src/MrGameEng.Simulation/AI/Suitability.cs
index 557a164..4e60e96 100644
--- a/src/MrGameEng.Simulation/AI/Suitability.cs
+++ b/src/MrGameEng.Simulation/AI/Suitability.cs
@@ -23,4 +23,41 @@ public static class Suitability
         var z = (value - optimum) / tolerance;
         return MathF.Exp(-0.5f * z * z);
     }
+
+    /// <summary>
+    /// Trapezoidal suitability in <c>[0, 1]</c>: <c>0</c> at or beyond the hard limits
+    /// <paramref name="min"/>/<paramref name="max"/>, ramping linearly up to <c>1</c> at
+    /// <paramref name="optimalLow"/>, flat <c>1</c> across the comfortable plateau to
+    /// <paramref name="optimalHigh"/>, then ramping back down to <c>0</c> at <paramref name="max"/>.
+    /// Models a hard tolerance band with a plateau (RimWorld-style plant growth vs. temperature:
+    /// dormant below <paramref name="min"/> or above <paramref name="max"/>). A degenerate edge
+    /// (<paramref name="optimalLow"/> ≤ <paramref name="min"/> or <paramref name="optimalHigh"/> ≥
+    /// <paramref name="max"/>) becomes a hard step on that side. The four bounds are expected
+    /// ordered (<c>min ≤ optimalLow ≤ optimalHigh ≤ max</c>); pass ordered values.
+    /// </summary>
+    public static float Trapezoid(
+        float value,
+        float min,
+        float optimalLow,
+        float optimalHigh,
+        float max
+    )
+    {
+        if (value <= min || value >= max)
+        {
+            return 0f;
+        }
+
+        if (value < optimalLow)
+        {
+            return optimalLow > min ? (value - min) / (optimalLow - min) : 1f;
+        }
+
+        if (value > optimalHigh)
+        {
+            return max > optimalHigh ? (max - value) / (max - optimalHigh) : 1f;
+        }
+
+        return 1f;
+    }
 }
diff --git a/tests/MrGameEng.Simulation.Tests/AI/SuitabilityTests.cs b/tests/MrGameEng.Simulation.Tests/AI/SuitabilityTests.cs
index d61fe99..cc50cbd 100644
--- a/tests/MrGameEng.Simulation.Tests/AI/SuitabilityTests.cs
+++ b/tests/MrGameEng.Simulation.Tests/AI/SuitabilityTests.cs
@@ -48,4 +48,45 @@ public class SuitabilityTests
         Assert.Equal(1f, Suitability.Gaussian(5f, 5f, 0f));
         Assert.Equal(0f, Suitability.Gaussian(6f, 5f, 0f));
     }
+
+    [Fact]
+    public void Trapezoid_IsFlatAcrossThePlateau()
+    {
+        Assert.Equal(1f, Suitability.Trapezoid(10f, 0f, 10f, 42f, 58f), 5);
+        Assert.Equal(1f, Suitability.Trapezoid(25f, 0f, 10f, 42f, 58f), 5);
+        Assert.Equal(1f, Suitability.Trapezoid(42f, 0f, 10f, 42f, 58f), 5);
+    }
+
+    [Fact]
+    public void Trapezoid_RampsLinearlyOnEachShoulder()
+    {
+        Assert.Equal(0.5f, Suitability.Trapezoid(5f, 0f, 10f, 42f, 58f), 5); // halfway up the cold ramp
+        Assert.Equal(0.5f, Suitability.Trapezoid(50f, 0f, 10f, 42f, 58f), 5); // halfway down the heat ramp
+    }
+
+    [Fact]
+    public void Trapezoid_IsZeroAtAndBeyondTheHardLimits()
+    {
+        Assert.Equal(0f, Suitability.Trapezoid(0f, 0f, 10f, 42f, 58f));
+        Assert.Equal(0f, Suitability.Trapezoid(-5f, 0f, 10f, 42f, 58f));
+        Assert.Equal(0f, Suitability.Trapezoid(58f, 0f, 10f, 42f, 58f));
+        Assert.Equal(0f, Suitability.Trapezoid(70f, 0f, 10f, 42f, 58f));
+    }
+
+    [Fact]
+    public void Trapezoid_DegenerateShoulder_IsAHardStep()
+    {
+        // optimalLow == min: full suitability immediately above the lower limit, zero at/below it.
+        Assert.Equal(1f, Suitability.Trapezoid(5f, 0f, 0f, 10f, 20f));
+        Assert.Equal(0f, Suitability.Trapezoid(0f, 0f, 0f, 10f, 20f));
+    }
+
+    [Fact]
+    public void Trapezoid_StaysWithinUnitRange()
+    {
+        for (var v = -50f; v <= 80f; v += 1f)
+        {
+            Assert.InRange(Suitability.Trapezoid(v, 0f, 10f, 42f, 58f), 0f, 1f);
+        }
+    }
 }