diff --git a/content/zettels/heaters.md b/content/zettels/heaters.md
index bb47ae7..0eb4954 100644
--- a/content/zettels/heaters.md
+++ b/content/zettels/heaters.md
@@ -8,10 +8,10 @@ Tags
 :
 
 
+## Commercial products {#commercial-products}
 
-<https://www.tcdirect.fr/product-2-300-1/Cartouche-chauffante>
-
-<https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=305>
+-   <https://www.tcdirect.fr/product-2-300-1/Cartouche-chauffante>
+-   <https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=305>
 
 
 ### Cryogenic temperature (~120K, UHV compatible) {#cryogenic-temperature--120k-uhv-compatible}