diff --git a/core/modules/responsive_image/lib/Drupal/responsive_image/Entity/ResponsiveImageMapping.php b/core/modules/responsive_image/lib/Drupal/responsive_image/Entity/ResponsiveImageMapping.php
index 658ad5d..b4fb7fc 100644
--- a/core/modules/responsive_image/lib/Drupal/responsive_image/Entity/ResponsiveImageMapping.php
+++ b/core/modules/responsive_image/lib/Drupal/responsive_image/Entity/ResponsiveImageMapping.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Definition of Drupal\responsive_image\ResponsiveImageMapping.
+ * Contains \Drupal\responsive_image\Entity\ResponsiveImageMapping.
  */
 
 namespace Drupal\responsive_image\Entity;
@@ -59,14 +59,14 @@ class ResponsiveImageMapping extends ConfigEntityBase implements ResponsiveImage
    *
    * @var array
    */
-  public $mappings = array();
+  protected $mappings = array();
 
   /**
    * The responsive image breakpoint group.
    *
-   * @var BreakpointGroup
+   * @var Drupal\breakpoint\Entity\BreakpointGroup
    */
-  public $breakpointGroup = '';
+  protected $breakpointGroup = '';
 
   /**
    * Overrides Drupal\config\ConfigEntityBase::__construct().
@@ -97,8 +97,9 @@ public function calculateDependencies() {
    */
   public function save() {
     // Only save the keys, but return the full objects.
-    if (isset($this->breakpointGroup) && is_object($this->breakpointGroup)) {
-      $this->breakpointGroup = $this->breakpointGroup->id();
+    $breakpoint_group = $this->getBreakpointGroup();
+    if ($breakpoint_group && is_object($breakpoint_group)) {
+      $this->setBreakpointGroup($breakpoint_group->id());
     }
 
     // Split the breakpoint ids into their different parts, as dots as
@@ -122,7 +123,7 @@ public function createDuplicate() {
     return entity_create('responsive_image_mapping', array(
       'id' => '',
       'label' => t('Clone of !label', array('!label' => check_plain($this->label()))),
-      'mappings' => $this->mappings,
+      'mappings' => $this->getMappings(),
     ));
   }
 
@@ -130,9 +131,9 @@ public function createDuplicate() {
    * Loads the breakpoint group.
    */
   protected function loadBreakpointGroup() {
-    if ($this->breakpointGroup) {
-      $breakpoint_group = entity_load('breakpoint_group', $this->breakpointGroup);
-      $this->breakpointGroup = $breakpoint_group;
+    if ($this->getBreakpointGroup()) {
+      $breakpoint_group = entity_load('breakpoint_group', $this->getBreakpointGroup());
+      $this->setBreakpointGroup($breakpoint_group);
     }
   }
 
@@ -140,33 +141,34 @@ protected function loadBreakpointGroup() {
    * Loads all mappings and removes non-existing ones.
    */
   protected function loadAllMappings() {
-    $loaded_mappings = $this->mappings;
-    $this->mappings = array();
-    if ($this->breakpointGroup) {
-      foreach ($this->breakpointGroup->getBreakpoints() as $breakpoint_id => $breakpoint) {
+    $loaded_mappings = $this->getMappings();
+    $all_mappings = array();
+    if ($breakpoint_group = $this->getBreakpointGroup()) {
+      foreach ($breakpoint_group->getBreakpoints() as $breakpoint_id => $breakpoint) {
         // Get the components of the breakpoint ID to match the format of the
         // configuration file.
         list($source_type, $source, $name) = explode('.', $breakpoint_id);
 
         // Get the mapping for the default multiplier.
-        $this->mappings[$breakpoint_id]['1x'] = '';
+        $all_mappings[$breakpoint_id]['1x'] = '';
         if (isset($loaded_mappings[$source_type][$source][$name]['1x'])) {
-          $this->mappings[$breakpoint_id]['1x'] = $loaded_mappings[$source_type][$source][$name]['1x'];
+          $all_mappings[$breakpoint_id]['1x'] = $loaded_mappings[$source_type][$source][$name]['1x'];
         }
 
         // Get the mapping for the other multipliers.
         if (isset($breakpoint->multipliers) && !empty($breakpoint->multipliers)) {
           foreach ($breakpoint->multipliers as $multiplier => $status) {
             if ($status) {
-              $this->mappings[$breakpoint_id][$multiplier] = '';
+              $all_mappings[$breakpoint_id][$multiplier] = '';
               if (isset($loaded_mappings[$source_type][$source][$name][$multiplier])) {
-                $this->mappings[$breakpoint_id][$multiplier] = $loaded_mappings[$source_type][$source][$name][$multiplier];
+                $all_mappings[$breakpoint_id][$multiplier] = $loaded_mappings[$source_type][$source][$name][$multiplier];
               }
             }
           }
         }
       }
     }
+    $this->setMappings($all_mappings);
   }
 
   /**
@@ -174,7 +176,7 @@ protected function loadAllMappings() {
    */
   public function hasMappings() {
     $mapping_found = FALSE;
-    foreach ($this->mappings as $multipliers) {
+    foreach ($this->getMappings() as $multipliers) {
       $filtered_array = array_filter($multipliers);
       if (!empty($filtered_array)) {
         $mapping_found = TRUE;
@@ -183,4 +185,52 @@ public function hasMappings() {
     }
     return $mapping_found;
   }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function toArray() {
+    $names = array(
+      'id',
+      'uuid',
+      'label',
+      'mappings',
+      'breakpointGroup',
+    );
+    $properties = array();
+    foreach ($names as $name) {
+      $properties[$name] = $this->get($name);
+    }
+    return $properties;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setMappings(array $mappings) {
+    $this->set('mappings', $mappings);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getMappings() {
+    return $this->get('mappings');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setBreakpointGroup($breakpoint_group) {
+    $this->set('breakpointGroup', $breakpoint_group);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getBreakpointGroup() {
+    return $this->get('breakpointGroup');
+  }
 }
diff --git a/core/modules/responsive_image/lib/Drupal/responsive_image/Plugin/Field/FieldFormatter/ResponsiveImageFormatter.php b/core/modules/responsive_image/lib/Drupal/responsive_image/Plugin/Field/FieldFormatter/ResponsiveImageFormatter.php
index 8f935c0..efbec0f 100644
--- a/core/modules/responsive_image/lib/Drupal/responsive_image/Plugin/Field/FieldFormatter/ResponsiveImageFormatter.php
+++ b/core/modules/responsive_image/lib/Drupal/responsive_image/Plugin/Field/FieldFormatter/ResponsiveImageFormatter.php
@@ -129,16 +129,16 @@ public function viewElements(FieldItemListInterface $items) {
 
     $responsive_image_mapping = entity_load('responsive_image_mapping', $this->getSetting('responsive_image_mapping'));
     if ($responsive_image_mapping) {
-      foreach ($responsive_image_mapping->mappings as $breakpoint_name => $multipliers) {
+      foreach ($responsive_image_mapping->getMappings() as $breakpoint_name => $multipliers) {
         // Make sure there are multipliers.
         if (!empty($multipliers)) {
           // Make sure that the breakpoint exists and is enabled.
           // @todo add the following when breakpoint->status is added again:
           // $responsive_image_mapping->breakpointGroup->breakpoints[$breakpoint_name]->status
-          $breakpoint = $responsive_image_mapping->breakpointGroup->getBreakpointById($breakpoint_name);
-          if ($breakpoint) {
+          $breakpointGroup = $responsive_image_mapping->getBreakpointGroup()->getBreakpointById($breakpoint_name);
+          if ($breakpointGroup) {
             // Determine the enabled multipliers.
-            $multipliers = array_intersect_key($multipliers, $breakpoint->multipliers);
+            $multipliers = array_intersect_key($multipliers, $breakpointGroup->multipliers);
             foreach ($multipliers as $multiplier => $image_style) {
               // Make sure the multiplier still exists.
               if (!empty($image_style)) {
diff --git a/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingFormController.php b/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingFormController.php
index d27db52..9b5e9c3 100644
--- a/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingFormController.php
+++ b/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingFormController.php
@@ -36,6 +36,7 @@ public function form(array $form, array &$form_state) {
       $form['#title'] = $this->t('<em>Edit responsive image mapping</em> @label', array('@label' => $this->entity->label()));
     }
 
+    /** @var \Drupal\responsive_image\ResponsiveImageMappingInterface $responsive_image_mapping */
     $responsive_image_mapping = $this->entity;
     $form['label'] = array(
       '#type' => 'textfield',
@@ -64,16 +65,16 @@ public function form(array $form, array &$form_state) {
     $form['breakpointGroup'] = array(
       '#type' => 'select',
       '#title' => $this->t('Breakpoint group'),
-      '#default_value' => !empty($responsive_image_mapping->breakpointGroup) ? $responsive_image_mapping->breakpointGroup->id() : '',
+      '#default_value' => ($responsive_image_mapping->getBreakpointGroup() != '') ? $responsive_image_mapping->getBreakpointGroup()->id() : '',
       '#options' => breakpoint_group_select_options(),
       '#required' => TRUE,
       '#description' => $description,
     );
 
     $image_styles = image_style_options(TRUE);
-    foreach ($responsive_image_mapping->mappings as $breakpoint_id => $mapping) {
+    foreach ($responsive_image_mapping->getMappings() as $breakpoint_id => $mapping) {
       foreach ($mapping as $multiplier => $image_style) {
-        $breakpoint = $responsive_image_mapping->breakpointGroup->getBreakpointById($breakpoint_id);
+        $breakpoint = $responsive_image_mapping->getBreakpointGroup()->getBreakpointById($breakpoint_id);
         $label = $multiplier . ' ' . $breakpoint->name . ' [' . $breakpoint->mediaQuery . ']';
         $form['mappings'][$breakpoint_id][$multiplier] = array(
           '#type' => 'select',
@@ -113,11 +114,12 @@ protected function actions(array $form, array &$form_state) {
    * Overrides Drupal\Core\Entity\EntityFormController::validate().
    */
   public function validate(array $form, array &$form_state) {
+    /** @var \Drupal\responsive_image\ResponsiveImageMappingInterface $responsive_image_mapping */
     $responsive_image_mapping = $this->entity;
 
     // Only validate on edit.
     if (isset($form_state['values']['mappings'])) {
-      $responsive_image_mapping->mappings = $form_state['values']['mappings'];
+      $responsive_image_mapping->setMappings($form_state['values']['mappings']);
 
       // Check if another breakpoint group is selected.
       if ($form_state['values']['breakpointGroup'] != $form_state['complete_form']['breakpointGroup']['#default_value']) {
@@ -135,6 +137,7 @@ public function validate(array $form, array &$form_state) {
    * Overrides Drupal\Core\Entity\EntityFormController::save().
    */
   public function save(array $form, array &$form_state) {
+    /** @var \Drupal\responsive_image\ResponsiveImageMappingInterface $responsive_image_mapping */
     $responsive_image_mapping = $this->entity;
     $responsive_image_mapping->save();
 
diff --git a/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingInterface.php b/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingInterface.php
index 2ec9832..bb8b535 100644
--- a/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingInterface.php
+++ b/core/modules/responsive_image/lib/Drupal/responsive_image/ResponsiveImageMappingInterface.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains \Drupal\responsive_image\Entity\ResponsiveImageMappingInterface.
+ * Contains \Drupal\responsive_image\ResponsiveImageMappingInterface.
  */
 
 namespace Drupal\responsive_image;
@@ -10,13 +10,55 @@
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
 
 /**
- * Provides an interface defining a responsive image mapping entity.
+ * Provides an interface defining a responsive_image mapping entity.
  */
 interface ResponsiveImageMappingInterface extends ConfigEntityInterface {
 
   /**
-   * Checks if there's at least one mapping defined.
+   * Checks if there is at least one mapping defined.
+   *
+   * return bool
+   *   Whether the entity has any responsive_image mappings.
    */
   public function hasMappings();
 
+  /**
+   * Sets the mappings for the responsive_image mapping.
+   *
+   * The array is keyed by the Breakpoint Group Id and then then by each
+   * Breakpoints multipliers within the Breakpoint Group.
+   *
+   * @param array[] $mappings
+   *   The mappings the responsive_image mapping will be set with.
+   *
+   * @return $this
+   */
+  public function setMappings(array $mappings);
+
+  /**
+   * Returns the mappings for the responsive_image mapping.
+   *
+   * @return array[]
+   *   The responsive_imagemappings.
+   */
+  public function getMappings();
+
+  /**
+   * Sets the breakpoint group for the responsive_image mapping.
+   *
+   * @param \Drupal\breakpoint\Entity\BreakpointGroup $breakpoint_group
+   *   The responsive_image mappings breakpoint group.
+   *
+   * @return $this
+   */
+  public function setBreakpointGroup($breakpoint_group);
+
+  /**
+   * Returns the breakpoint group for the responsive_image mapping.
+   *
+   * @return \Drupal\breakpoint\Entity\BreakpointGroup
+   *   The responsive_image mappings breakpoint group.
+   */
+  public function getBreakpointGroup();
+
 }
diff --git a/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php b/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php
index c643774..f580858 100644
--- a/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php
+++ b/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php
@@ -88,9 +88,11 @@ public function setUp() {
       'breakpointGroup' => 'atestset',
     ));
     $responsive_image_mapping->save();
-    $responsive_image_mapping->mappings['custom.user.small']['1x'] = 'thumbnail';
-    $responsive_image_mapping->mappings['custom.user.medium']['1x'] = 'medium';
-    $responsive_image_mapping->mappings['custom.user.large']['1x'] = 'large';
+    $mappings = array();
+    $mappings['custom.user.small']['1x'] = 'thumbnail';
+    $mappings['custom.user.medium']['1x'] = 'medium';
+    $mappings['custom.user.large']['1x'] = 'large';
+    $responsive_image_mapping->setMappings($mappings);
     $responsive_image_mapping->save();
   }