Thermal Undershirt
Accessory2★A worn layer that nudges Cold Resistance up a little.
Wearing it also carries the effect Cold Resistance Lv. 3, which matters more than the raw numbers in the biomes that punish you for the wrong outfit.
No recipe takes it as an ingredient. Whatever you build is the finished article, so there is no reason to hoard spares.
Details
It does not stack, so every spare copy costs an inventory slot. At 21,960 gold it is worth real money to a merchant.
Thermal Undershirt Crafting Recipe
Wool×20
Ice Organ×15
Leather×25
Cloth×10Crafting it takes 70 materials across 4 types.
Where to Find Thermal Undershirt
The recipe is not on the Technology tree — it is locked behind a schematic you have to find first. The best single source is treasure chests in the Feybreak at 3.4% per container, and the table below lists every tier and where each one drops.
There is a stronger copy, and no amount of farming Ice Organs will get you it. The Rare version is gated behind the Thermal Undershirt Schematic (Thermal Undershirt Schematic), a grade 5 chest item that exists nowhere outside Feybreak: 3.45% from treasure chests in Feybreak Cavern, 1.18% from the crates out on the oil rigs, 0.19% from ordinary Feybreak chests. That works out to about 29 cavern treasure chests, 85 rig crates or 526 field chests for one. Run the cavern. The field chests are the same paper for eighteen times the walking.
Using Thermal Undershirt Well
The schematic asks for a High-Quality Workbench, which is the bench this plain copy already uses, so picking one up costs you no extra base build. Note that the further plus tiers have no recipe attached anywhere in the crafting tables — they are pure loot, so the paper version is the last one you can decide to make.
Before you commit Ice Organs here, look at where you are heading. Multiclimate Undershirt carries this exact cold line and the heat line of Heat Resistant Undershirt together in a single slot, and it wants 20 Ice Organ anyway on top of 20 Fire Organs, 40 Refined Cloth and 20 Polymer — the game prices it at 167,040 against 21,960 for this. Both shirts weigh 2 and neither stacks, so hauling one of each to cover a mixed run costs you 4 weight and a swap in the field. Build this while the snowfield is the only place freezing you; skip straight past it if the volcano is already on your route and the Polymer is in reach.
What Thermal Undershirt Does
Thermal Undershirt grants Cold Resistance Lv. 3: Temperature Resist Cold +3.
Schematics That Unlock Thermal Undershirt
Thermal Undershirt is not learned from the Technology tree — you need a schematic for it. One schematic grants the recipe, and they are world loot — chests, boss Pals and the late-game pools — rather than anything you research. Higher-rarity copies of the same schematic raise the quality of what you end up crafting.
Fastest route. The top-tier Thermal Undershirt schematic is worth hunting directly — treasure chests in the Feybreak is its best source, at roughly 29 containers a copy. Schematics fuse five-to-one, so a lower tier with better odds can beat the top tier outright. Counts are containers of that source, not time.
| Schematic | Rarity | Where it comes from |
|---|---|---|
 Thermal Undershirt Schematic | 2★ | Feybreak treasure chests, Crates on the oil rigs, Feybreak chests — best 3.4% (grade 5) |
Alternatives and Upgrades
Other accessorys at a similar tier, for when you want to weigh this against the rest of its class:
