diff --git a/lighthouse-core/report/html/renderer/details-renderer.js b/lighthouse-core/report/html/renderer/details-renderer.js
index e2a506cfe98b..179b7eedd9e8 100644
--- a/lighthouse-core/report/html/renderer/details-renderer.js
+++ b/lighthouse-core/report/html/renderer/details-renderer.js
@@ -208,7 +208,7 @@ class DetailsRenderer {
    * Render a details item value for embedding in a table. Renders the value
    * based on the heading's valueType, unless the value itself has a `type`
    * property to override it.
-   * @param {LH.Audit.Details.TableItem[string] | LH.Audit.Details.OpportunityItem[string]} value
+   * @param {LH.Audit.Details.Value} value
    * @param {LH.Audit.Details.OpportunityColumnHeading} heading
    * @return {Element|null}
    */
@@ -246,7 +246,7 @@ class DetailsRenderer {
     switch (heading.valueType) {
       case 'bytes': {
         const numValue = Number(value);
-        return this._renderBytes({value: numValue, granularity: 1});
+        return this._renderBytes({value: numValue, granularity: heading.granularity});
       }
       case 'code': {
         const strValue = String(value);
@@ -296,22 +296,54 @@ class DetailsRenderer {
    * OpportunityColumnHeading type until we have all details use the same
    * heading format.
    * @param {LH.Audit.Details.Table|LH.Audit.Details.Opportunity} tableLike
-   * @return {Array<LH.Audit.Details.OpportunityColumnHeading>} header
+   * @return {Array<LH.Audit.Details.OpportunityColumnHeading>}
    */
-  _getCanonicalizedTableHeadings(tableLike) {
+  _getCanonicalizedHeadingsFromTable(tableLike) {
     if (tableLike.type === 'opportunity') {
       return tableLike.headings;
     }
 
-    return tableLike.headings.map(heading => {
-      return {
-        key: heading.key,
-        label: heading.text,
-        valueType: heading.itemType,
-        displayUnit: heading.displayUnit,
-        granularity: heading.granularity,
-      };
-    });
+    return tableLike.headings.map(heading => this._getCanonicalizedHeading(heading));
+  }
+
+  /**
+   * Get the headings of a table-like details object, converted into the
+   * OpportunityColumnHeading type until we have all details use the same
+   * heading format.
+   * @param {LH.Audit.Details.TableColumnHeading} heading
+   * @return {LH.Audit.Details.OpportunityColumnHeading}
+   */
+  _getCanonicalizedHeading(heading) {
+    let subRows;
+    if (heading.subRows) {
+      // @ts-ignore: It's ok that there is no text.
+      subRows = this._getCanonicalizedHeading(heading.subRows);
+    }
+
+    return {
+      key: heading.key,
+      valueType: heading.itemType,
+      subRows,
+      label: heading.text,
+      displayUnit: heading.displayUnit,
+      granularity: heading.granularity,
+    };
+  }
+
+  /**
+   * @param {LH.Audit.Details.Value[]} values
+   * @param {LH.Audit.Details.OpportunityColumnHeading} heading
+   * @return {Element}
+   */
+  _renderSubRows(values, heading) {
+    const subRowsElement = this._dom.createElement('div', 'lh-sub-rows');
+    for (const childValue of values) {
+      const subRowElement = this._renderTableValue(childValue, heading);
+      if (!subRowElement) continue;
+      subRowElement.classList.add('lh-sub-row');
+      subRowsElement.appendChild(subRowElement);
+    }
+    return subRowsElement;
   }
 
   /**
@@ -325,7 +357,7 @@ class DetailsRenderer {
     const theadElem = this._dom.createChildOf(tableElem, 'thead');
     const theadTrElem = this._dom.createChildOf(theadElem, 'tr');
 
-    const headings = this._getCanonicalizedTableHeadings(details);
+    const headings = this._getCanonicalizedHeadingsFromTable(details);
 
     for (const heading of headings) {
       const valueType = heading.valueType || 'text';
@@ -339,12 +371,30 @@ class DetailsRenderer {
     for (const row of details.items) {
       const rowElem = this._dom.createChildOf(tbodyElem, 'tr');
       for (const heading of headings) {
+        const valueFragment = this._dom.createFragment();
+
         const value = row[heading.key];
-        const valueElement = this._renderTableValue(value, heading);
+        const valueElement =
+          value !== undefined && !Array.isArray(value) && this._renderTableValue(value, heading);
+        if (valueElement) valueFragment.appendChild(valueElement);
+
+        if (heading.subRows) {
+          const subRowsHeading = {
+            key: heading.subRows.key,
+            valueType: heading.subRows.valueType || heading.valueType,
+            granularity: heading.subRows.granularity || heading.granularity,
+            displayUnit: heading.subRows.displayUnit || heading.displayUnit,
+            label: '',
+          };
+          const values = row[subRowsHeading.key];
+          if (!Array.isArray(values)) continue;
+          const subRowsElement = this._renderSubRows(values, subRowsHeading);
+          valueFragment.appendChild(subRowsElement);
+        }
 
-        if (valueElement) {
+        if (valueFragment.childElementCount) {
           const classes = `lh-table-column--${heading.valueType}`;
-          this._dom.createChildOf(rowElem, 'td', classes).appendChild(valueElement);
+          this._dom.createChildOf(rowElem, 'td', classes).appendChild(valueFragment);
         } else {
           this._dom.createChildOf(rowElem, 'td', 'lh-table-column--empty');
         }
diff --git a/lighthouse-core/report/html/report-styles.css b/lighthouse-core/report/html/report-styles.css
index 0ecb30f0317a..3408de2e7c05 100644
--- a/lighthouse-core/report/html/report-styles.css
+++ b/lighthouse-core/report/html/report-styles.css
@@ -167,6 +167,7 @@
     /* Pallete */
     --color-gray-200: var(--color-gray-800);
     --color-gray-400: var(--color-gray-600);
+    --color-gray-700: var(--color-gray-400);
     --color-gray-50: #757575;
     --color-gray-600: var(--color-gray-500);
     --color-green-700: var(--color-green);
@@ -1405,6 +1406,11 @@
   text-decoration: underline dotted #999;
 }
 
+.lh-sub-rows:not(:first-child) .lh-sub-row {
+  margin-left: 20px;
+  color: var(--color-gray-700);
+}
+
 /* Chevron
    https://codepen.io/paulirish/pen/LmzEmK
  */
diff --git a/lighthouse-core/test/report/html/renderer/details-renderer-test.js b/lighthouse-core/test/report/html/renderer/details-renderer-test.js
index 3dd2058b5ba5..0b4193ebd945 100644
--- a/lighthouse-core/test/report/html/renderer/details-renderer-test.js
+++ b/lighthouse-core/test/report/html/renderer/details-renderer-test.js
@@ -548,7 +548,7 @@ describe('DetailsRenderer', () => {
         // itemType is overriden by code object
         headings: [{key: 'content', itemType: 'url', text: 'Heading'}],
         items: [
-          {content: {type: 'code', value: 'code object'}},
+          {content: {type: 'code', value: 'https://codeobject.com'}},
           {content: 'https://example.com'},
         ],
       };
@@ -560,7 +560,7 @@ describe('DetailsRenderer', () => {
       const codeEl = itemElements[0].firstChild;
       assert.equal(codeEl.localName, 'pre');
       assert.ok(codeEl.classList.contains('lh-code'));
-      assert.equal(codeEl.textContent, 'code object');
+      assert.equal(codeEl.textContent, 'https://codeobject.com');
 
       // Second item uses the heading's specified type for the column.
       const urlEl = itemElements[1].firstChild;
@@ -569,5 +569,78 @@ describe('DetailsRenderer', () => {
       assert.equal(urlEl.title, 'https://example.com');
       assert.equal(urlEl.textContent, 'https://example.com');
     });
+
+    describe('subRows', () => {
+      it('renders', () => {
+        const details = {
+          type: 'table',
+          headings: [{key: 'url', itemType: 'url', subRows: {key: 'sources', itemType: 'code'}}],
+          items: [
+            {url: 'https://www.example.com', sources: ['a', 'b', 'c']},
+          ],
+        };
+
+        const el = renderer.render(details);
+        const columnElement = el.querySelector('td.lh-table-column--url');
+
+        // First element is the url.
+        const codeEl = columnElement.firstChild;
+        assert.equal(codeEl.localName, 'div');
+        assert.ok(codeEl.classList.contains('lh-text__url'));
+        assert.equal(codeEl.textContent, 'https://www.example.com');
+
+        // Second element lists the multiple values.
+        const subRowsEl = columnElement.children[1];
+        assert.equal(subRowsEl.localName, 'div');
+        assert.ok(subRowsEl.classList.contains('lh-sub-rows'));
+
+        const multiValueEls = subRowsEl.querySelectorAll('.lh-sub-row');
+        assert.equal(multiValueEls[0].textContent, 'a');
+        assert.ok(multiValueEls[0].classList.contains('lh-code'));
+        assert.equal(multiValueEls[1].textContent, 'b');
+        assert.ok(multiValueEls[1].classList.contains('lh-code'));
+        assert.equal(multiValueEls[2].textContent, 'c');
+        assert.ok(multiValueEls[2].classList.contains('lh-code'));
+      });
+
+      it('renders, uses heading properties as fallback', () => {
+        const details = {
+          type: 'table',
+          headings: [{key: 'url', itemType: 'url', subRows: {key: 'sources'}}],
+          items: [
+            {
+              url: 'https://www.example.com',
+              sources: [
+                'https://www.a.com',
+                {type: 'code', value: 'https://www.b.com'},
+                'https://www.c.com',
+              ],
+            },
+          ],
+        };
+
+        const el = renderer.render(details);
+        const columnElement = el.querySelector('td.lh-table-column--url');
+
+        // First element is the url.
+        const codeEl = columnElement.firstChild;
+        assert.equal(codeEl.localName, 'div');
+        assert.ok(codeEl.classList.contains('lh-text__url'));
+        assert.equal(codeEl.textContent, 'https://www.example.com');
+
+        // Second element lists the multiple values.
+        const subRowsEl = columnElement.children[1];
+        assert.equal(subRowsEl.localName, 'div');
+        assert.ok(subRowsEl.classList.contains('lh-sub-rows'));
+
+        const multiValueEls = subRowsEl.querySelectorAll('.lh-sub-row');
+        assert.equal(multiValueEls[0].textContent, 'https://www.a.com');
+        assert.ok(multiValueEls[0].classList.contains('lh-text__url'));
+        assert.equal(multiValueEls[1].textContent, 'https://www.b.com');
+        assert.ok(multiValueEls[1].classList.contains('lh-code'));
+        assert.equal(multiValueEls[2].textContent, 'https://www.c.com');
+        assert.ok(multiValueEls[2].classList.contains('lh-text__url'));
+      });
+    });
   });
 });
diff --git a/types/audit-details.d.ts b/types/audit-details.d.ts
index 6b1820afdbf6..b5dfef7de0f8 100644
--- a/types/audit-details.d.ts
+++ b/types/audit-details.d.ts
@@ -82,7 +82,8 @@ declare global {
       }
 
       /** Possible types of values found within table items. */
-      type ItemValueTypes = 'bytes' | 'code' | 'link' | 'ms' | 'node' | 'source-location' | 'numeric' | 'text' | 'thumbnail' | 'timespanMs' | 'url';
+      type ItemValueTypes = 'bytes' | 'code' | 'link' | 'ms' | 'multi' | 'node' | 'source-location' | 'numeric' | 'text' | 'thumbnail' | 'timespanMs' | 'url';
+      type Value = string | number | boolean | DebugData | NodeValue | SourceLocationValue | LinkValue | UrlValue | CodeValue;
 
       // TODO(bckenny): unify Table/Opportunity headings and items on next breaking change.
 
@@ -97,6 +98,11 @@ declare global {
          * could also be objects with their own type to override this field.
          */
         itemType: ItemValueTypes;
+        /**
+         * Optional - defines an inner table of values that correspond to this column.
+         * Key is required - if other properties are not provided, the value for the heading is used.
+         */
+        subRows?: {key: string, itemType?: ItemValueTypes, displayUnit?: string, granularity?: number};
 
         displayUnit?: string;
         granularity?: number;
@@ -104,7 +110,7 @@ declare global {
 
       export type TableItem = {
         debugData?: DebugData;
-        [p: string]: undefined | string | number | boolean | undefined | DebugData | NodeValue | SourceLocationValue | LinkValue | UrlValue | CodeValue;
+        [p: string]: undefined | Value | Value[];
       }
 
       export interface OpportunityColumnHeading {
@@ -118,6 +124,11 @@ declare global {
          * could also be objects with their own type to override this field.
          */
         valueType: ItemValueTypes;
+        /**
+         * Optional - defines an inner table of values that correspond to this column.
+         * Key is required - if other properties are not provided, the value for the heading is used.
+         */
+        subRows?: {key: string, valueType?: ItemValueTypes, displayUnit?: string, granularity?: number};
 
         // NOTE: not used by opportunity details, but used in the renderer until table/opportunity unification.
         displayUnit?: string;
@@ -130,7 +141,7 @@ declare global {
         totalBytes?: number;
         wastedMs?: number;
         debugData?: DebugData;
-        [p: string]: number | boolean | string | undefined | DebugData;
+        [p: string]: undefined | Value | Value[];
       }
 
       /**