The Thaumium Fortress Helm is an armor added by Thaumcraft 6. It is an advanced version of the Thaumium Helm; it has greater durability, rating, and protection from magic, fire or explosion damage. Additionally, when wearing multiple pieces of the Thaumium Fortress set, the damage reduction increases. The helmet also gives 3 armor toughness points.
Thaumium armor has many things to recommend it, but its basic construction leaves it inferior to diamond armor. By improving the construction process and complexity you have found a way to create armor of exceptional craftsmanship, durability and strength. Each individual piece of Thaumium Fortress armor has the same protective properties as diamond armor, but has greater durability and offers additional protection against magic and fire. The biggest benefit however is that the individual armor pieces is designed and constructed to be worn together: Each additional piece of this armor worn increases the overall protection offered by all other pieces and improves its visual appeal. As with most objects constructed from thaumium, the armor is easy to enchant.