The FU economy

FU is denominated by tier: a T5 spool stores T5 FU, a T1 spool stores T1 FU. One unit of Tier N FU is worth several units of Tier N-1 (the conversion ratio is set in config). Tier is value, not just capacity, and every spool T1–T8 holds a uniform 100,000 FU.

Where costs come from

Each block’s FU cost and tier are derived from its recipe graph: crafting, plus optionally smelting and stonecutting. A diamond block costs what its diamonds are worth; stone costs almost nothing. A block’s material tier sets the minimum machine and spool tier needed to print it.

Two different rules

The whole economy runs on two rules, and everything else follows from them:

• Winding (making FU) is exact-tier. A material winds only into a spool of its own tier. Covered in Filament Units.
• Spending (printing) is down-only. A spool pays any cost at or below its tier, never above.

What that gets you

Put those together and matter becomes interchangeable within a tier. Sculk and diamond are both T5, so a T5 spool wound from sculk prints diamonds. Copper and gold are both T2, so your useless copper pile prints gold. Nothing special implements this; it is just what the two rules mean.

Down-only spending extends it in one direction: a high-tier spool also pays for anything beneath it, so a T6 spool can print gold, redstone, and stone all day.

Ratios are at exact break-even, which needs a Tier 4+ machine; see the markup below. Doing this in practice is Item Mode.

What it stops

The same two rules are the anti-exploit gate. Converting upward is impossible: low-tier filament contributes nothing toward a higher-tier cost, so a T1 spool can never print netherite no matter how much cobblestone you feed it. A cobblestone farm stays a cobblestone farm.

The markup

Lower-tier machines pay a higher FU multiplier per block, and printing always costs a little more than the matter is worth. Stack 4 Efficiency modules to reach exact break-even (1:1), which only a Tier 4+ machine has the slots for. You can never print matter for less than it’s worth. See upgrades for module slots.

Printing food

Food has FU values too, so a printer in Item Mode can print meals: bread is cheap, cooked and golden food cost more. But food can’t be wound back into FU, so printing food is a one-way sink, not a loop.

Restricted trophies

Mob heads and skulls are trophy items: printers never duplicate them in item mode, and in blueprint mode they place only from an official curated blueprint that specifically carries them (like the Pig House’s decorative heads). A scanned or imported build containing a head prints everything else and silently skips the trophy, the same anti-exploit gate as resins.

Heads still wind, though. Creeper, zombie, skeleton, and piglin heads recycle into Tier 4 Filament Units, so charged-creeper trophies aren’t a dead end. The wither skeleton skull is the exception: it winds for a Tier 4 payout but is wind-only (never printed, in any mode), so a wither-skeleton farm can’t mint printable wither-spawn ingredients.

When a mod makes a trophy farmable

Nether stars and dragon eggs are priced as one-off trophies: 1,500 and 10,000 Filament Units, at the top of the tier ladder. That only holds because you can’t farm them.

Mystical Agradditions adds crops for both, so when it’s installed MC3DPrint stops accepting them at the winder. A Tier 7 spool prints everything at Tier 7 and below, and a renewable Tier 7 payout would make the whole ladder free.

Only winding changes. The nether star is still an ordinary item you can craft with that mod, build beacons from, and print from a Tier 7 machine. The dragon egg is still a placeable trophy block, and it was already wind-only, so all it loses is the recycle payout. Install Mystical Agradditions and you get an infinite supply of nether stars for beacons, just not an infinite supply of filament.

Insanium is handled separately: it can be neither wound nor printed. It sits one crafting step above supremium, which would hand a farm a Tier 5 payout for free. It stays a completely normal Mystical Agradditions item, MC3DPrint just doesn’t participate. One consequence worth knowing: a scanned build containing insanium blocks prints everything else and leaves those spaces empty, the same way it handles any block it won’t reproduce.

Without Mystical Agradditions, none of this applies and both trophies wind exactly as before. This is the only place where an optional mod’s presence changes how MC3DPrint treats a vanilla item.