diff --git a/.travis.yml b/.travis.yml
index 93657e5..adc6274 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -40,3 +40,6 @@ install:
 
 script:
   - make test
+
+after_script:
+  - make prune
diff --git a/docs/openapi.yml b/docs/openapi.yml
index 59476c7..7ddec7c 100644
--- a/docs/openapi.yml
+++ b/docs/openapi.yml
@@ -62,12 +62,14 @@ components:
       allOf:
         # Inherit PutRunningSession
         - $ref: '#/components/schemas/PutRunningSession'
-      required: [ temperatureCelcius ]
+      required: [ temperatureCelcius, is_freezing ]
       properties:
         temperatureCelcius:
           type: number
           format: float
           example: 37.2
+        is_freezing:
+          type: boolean
 
     RunningSessionId:
       type: integer
diff --git a/src/Application/Command/RegisterRunningSessionHandler.php b/src/Application/Command/RegisterRunningSessionHandler.php
index b959e03..0863c78 100644
--- a/src/Application/Command/RegisterRunningSessionHandler.php
+++ b/src/Application/Command/RegisterRunningSessionHandler.php
@@ -6,6 +6,7 @@
 
 use App\Domain\RunningSession;
 use App\Domain\RunningSessionRepository;
+use App\Domain\Temperature;
 use App\Domain\WeatherProvider;
 
 class RegisterRunningSessionHandler
@@ -27,7 +28,7 @@ public function handle(RegisterRunningSession $command): RunningSession
             $command->getId(),
             $command->getDistance(),
             $command->getShoes(),
-            $currentTemperature
+            new Temperature($currentTemperature)
         );
 
         $this->repository->add($session);
diff --git a/src/Domain/RunningSession.php b/src/Domain/RunningSession.php
index d8b11ac..3d42db4 100644
--- a/src/Domain/RunningSession.php
+++ b/src/Domain/RunningSession.php
@@ -9,14 +9,14 @@ class RunningSession
     private int $id;
     private float $distance;
     private string $shoes;
-    private float $metricTemperature;
+    private Temperature $temperature;
 
-    public function __construct(int $id, float $distance, string $shoes, float $metricTemperature)
+    public function __construct(int $id, float $distance, string $shoes, Temperature $temperature)
     {
         $this->id = $id;
         $this->distance = $distance;
         $this->shoes = $shoes;
-        $this->metricTemperature = $metricTemperature;
+        $this->temperature = $temperature;
     }
 
     public function getId(): int
@@ -36,6 +36,11 @@ public function getShoes(): string
 
     public function getMetricTemperature(): float
     {
-        return $this->metricTemperature;
+        return $this->temperature->getMetricTemperature();
+    }
+
+    public function isFreezing(): bool
+    {
+        return $this->temperature->isFreezing();
     }
 }
diff --git a/src/Domain/Temperature.php b/src/Domain/Temperature.php
new file mode 100644
index 0000000..648aa4a
--- /dev/null
+++ b/src/Domain/Temperature.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Domain;
+
+use Webmozart\Assert\Assert;
+
+class Temperature
+{
+    private const ABSOLUTE_ZERO = -273.15;
+
+    private float $metricTemperature;
+
+    public function __construct(float $metricTemperature)
+    {
+        Assert::greaterThanEq(
+            $metricTemperature,
+            self::ABSOLUTE_ZERO,
+            "Cannot create temperature below absolute zero: $metricTemperature"
+        );
+
+        $this->metricTemperature = $metricTemperature;
+    }
+
+    public function getMetricTemperature(): float
+    {
+        return $this->metricTemperature;
+    }
+
+    public function isFreezing(): bool
+    {
+        return $this->metricTemperature < 0;
+    }
+}
diff --git a/src/Infrastructure/Symfony/Serializer/RunningSessionSerializer.php b/src/Infrastructure/Symfony/Serializer/RunningSessionSerializer.php
index b571349..dc484b8 100644
--- a/src/Infrastructure/Symfony/Serializer/RunningSessionSerializer.php
+++ b/src/Infrastructure/Symfony/Serializer/RunningSessionSerializer.php
@@ -18,6 +18,7 @@ public function serialize(RunningSession $session): string
             'distance' => $session->getDistance(),
             'shoes' => $session->getShoes(),
             'temperatureCelcius' => $session->getMetricTemperature(),
+            'is_freezing' => $session->isFreezing(),
         ];
 
         return json_encode($data, JSON_THROW_ON_ERROR);
diff --git a/tests/Domain/RunningSessionFactory.php b/tests/Domain/RunningSessionFactory.php
index 753f284..c26c12d 100644
--- a/tests/Domain/RunningSessionFactory.php
+++ b/tests/Domain/RunningSessionFactory.php
@@ -12,6 +12,6 @@ public static function create(
         string $shoes = 'shoes_value_not_used',
         float $metricTemperature = 98.76
     ): RunningSession {
-        return new RunningSession($id, $distance, $shoes, $metricTemperature);
+        return new RunningSession($id, $distance, $shoes, new Temperature($metricTemperature));
     }
 }
diff --git a/tests/Domain/TemperatureTest.php b/tests/Domain/TemperatureTest.php
new file mode 100644
index 0000000..4e61421
--- /dev/null
+++ b/tests/Domain/TemperatureTest.php
@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Domain;
+
+use PHPUnit\Framework\TestCase;
+
+class TemperatureTest extends TestCase
+{
+    public function testIsNotFreezingAboveZero()
+    {
+        //Given
+        $temperature = new Temperature(25.7);
+
+        //When
+        $result = $temperature->isFreezing();
+
+        //Then
+        self::assertFalse($result, 'temperature should not be freezing');
+    }
+
+    public function testIsFreezingBelowZero()
+    {
+        //Given
+        $temperature = new Temperature(-12);
+
+        //When
+        $result = $temperature->isFreezing();
+
+        //Then
+        self::assertTrue($result, 'temperature should be freezing');
+    }
+}
diff --git a/tests/Infrastructure/Symfony/Serializer/RunningSessionSerializerTest.php b/tests/Infrastructure/Symfony/Serializer/RunningSessionSerializerTest.php
index d910229..367b22d 100644
--- a/tests/Infrastructure/Symfony/Serializer/RunningSessionSerializerTest.php
+++ b/tests/Infrastructure/Symfony/Serializer/RunningSessionSerializerTest.php
@@ -29,7 +29,8 @@ public function testRunningSessionIsConvertedToJson()
   "id": 42,
   "distance": 5.5,
   "shoes": "Adadis Turbo2",
-  "temperatureCelcius": 37.2
+  "temperatureCelcius": 37.2,
+  "is_freezing": false
 }
 EOD;
         self::assertJsonStringEqualsJsonString($expectedJson, $result);