The Dense Glass is a block added by Deep Resonance. It is very resistant to explosions and each block of Dense Glass Radiation has to pass through to reach a certain position will reduce its strength by 90% at that position.
Obsidian helps to block some of the radiation but dense obsidian is even better. You can also use lead blocks. These are better then obsidian but not as good as dense obsidian. Dense glass is about as good as lead.