diff --git a/book/basics/concrete/information.ipynb b/book/basics/concrete/information.ipynb
index 27179a4..0ca2469 100644
--- a/book/basics/concrete/information.ipynb
+++ b/book/basics/concrete/information.ipynb
@@ -4,7 +4,19 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# Information"
+    "# Information\n",
+    "\n",
+    "## Different sources\n",
+    "\n",
+    "  - **Internet**\n",
+    "    - [VBI.nl](https://www.vbi.nl/): Hollow core slabs and system floors (only in Dutch)\n",
+    "    - [Spanbeton.nl](https://www.spanbeton.nl/): Large prefab elements used in road- and railway construction, hydraulic engineering, industrial buildings, and concrete sheet piling (only in Dutch)\n",
+    "    - [Dycore.nl](https://www.dycore.nl/): Different floor systems. CAD drawings and details can be downloaded. Design graphs are available (only in Dutch)\n",
+    "    - [Bubbledeck.nl](https://www.bubbledeck.nl/): The new bubble-deck system to construct lighter floors (only in Dutch)\n",
+    "    - [Haitsma.nl](https://www.haitsma.nl/): Bridges, foundations, offices, parking lots. CAD details and design graphs (only in Dutch)\n",
+    "    - [Koraton.be](https://www.koraton.be/): Different system floors (in Dutch or French)\n",
+    "    - [Heidelbergcement.com](https://www.heidelbergcement.com/): General information on cement and concrete (most languages available)\n",
+    "  - **Magazines**: Cement projects, elements, and materials\n"
    ]
   },
   {