Explosives

Explosives need a Workbench Level 3 and its blueprint (500 scrap on the tech tree). One batch costs Gun Powder, Low Grade Fuel, Sulfur and Metal Fragments, and takes 5 seconds to craft — the actual bottleneck is farming enough Gun Powder, not the craft itself.

Gun Powder is most of the cost

Fifty Gun Powder per batch means Explosives inherit gunpowder's own bottleneck — sulfur. If you haven't got your sulfur income sorted, that's the thing to fix before you worry about anything else in this recipe; see the gunpowder guide on this site for that half of the chain.

The other three ingredients

Low Grade Fuel, Sulfur and Metal Fragments are all things you're likely already stockpiling for other recipes, so once the workbench and blueprint are sorted, a batch of Explosives is mostly a matter of having enough raw sulfur banked rather than a separate farming trip.

What it's actually for

Explosives don't do anything on their own — they're the shared input for C4, Rockets and Explosive 5.56 Ammo. Farming Explosives in bulk before a raid, rather than crafting each explosive type from scratch as you go, is the standard approach since it lets you decide what to turn them into at the last second.