How to get Flame Sac in Monster Hunter Wilds
Where to find Flame Sac.
Flame Sac in Monster Hunter Wilds is a type of material that's worth collecting as it comes off a high-tier monster.
Just like Aqua Sac, Flame Sac in Monster Hunter Wilds comes off one of the large monsters you'll face in-game. However, if you're looking for this material before you reach Chapter 3 of the main story then you will not find it as its monster only spawns for the first time during this section.
On that note, here's how to get Flame Sac in Monster Hunter Wilds.
How to get Flame Sac in Monster Hunter Wilds
In Monster Hunter Wilds you get Flame Sac from slaying Guardian Rathalos which can only be found in Wyveria.
When it opens up to you, you can also do the 'His Eternal Reign' optional quest to hunt a Guardian Rathalos and be rewarded with Flame Sac upon completion as a quest reward, as well as having the chance to harvest it from the carcass of this monster too.

Guardian Rathalos are a large monster and they can be tricky to defeat, they're more feriocious than their non-guardian relatives and you're often fighting them in a small space, which restricts your options when it comes to avoiding incoming attacks.
To help you slay a Guardian Rathalos to get a Flame Sac you should use Dragon-based or Thunder-based elemental attacks as they're weak to these elements. This includes Dragon Pods and Thunder Pods for your slinger. Also, the Guardian Rathalos' weak points are its mouth and legs. Both wings are breakable and the tail is severable, meaning you've got plenty of choices when it comes to deciding where to target.

When you've defeated a Guaridan Rathalos you need to harvest materials from its carcass. Now, you're not always guarunteed to get a Flame Sac each time you do this, but you're more likely to get this material if you're doing a quest hunt for this monster.
That's all for now! If you're looking for more Monster Hunter Wilds content, check out our pages showing you how to get Wingdrake Hide, where to get Herbivore Shell and how to catch a Gravid Bowfin.