Staying Dry in Prologue: Go Wayback! Inside Our Dynamic Wetness System
May 16, 2025
How does a rain-shower turn from gentle environmental ambience into a genuine survival hazard? What happens when every object you carry remembers exactly how much water it has soaked up? PLAYERUNKNOWN Productions' upcoming survival game Prologue: Go Wayback! sets the player against the forces of nature. Because our new Wetness System tracks water absorption and evaporation for every item the player owns, in our ML generated landscapes a drizzle could tip the balance from comfort to hypothermia. Today we take you under the hood to show how a few simple physical principles we’ve implemented to create meaningful, emergent choices for every run.
In this article we will explain the variables that drive Wetness, show how they interact with other survival systems such as temperature and fire-lighting, and share practical tips for staying (mostly) dry. If you would like to discuss the details—or have fun ideas we should test—join our community on Discord where we run regular playtests, and use feedback to help shape each next iteration of our game.
Author: Yoan Rock, Unreal Gameplay Programmer at PLAYERUNKNOWN Productions.
Why Wetness Matters
As with all of the effects and objects in our game world, rain, rivers and humidity are not just visual effects; they have a direct impact on the player’s heat, a damp log refuses to ignite, and a soaked jacket can leach warmth faster than the wind can dry it out. Go Wayback! is a hard game because of the layered systems that connect player choices to survival consequences.
Rain in Go Wayback! Image credit to community member and virtual photographer, 5qu34k.
Wetness in the World
In our initial implementation wetness is be calculated based on four factors:
- Waterproofness (of the item)
- Weather (rain, overcast)
- Wind
- Temperature
With these factors in mind we can start imagining and creating rules for how different scenarios can impact Wetness. For instance in Go Wayback! the last two factors, Wind and Temperature, depend on whether the player is outside (world temperature) or inside (shelter temperature). If the shelter is broken, and the wind and weather can rush in, it will be treated as "outside" for the wetness system. Each item checks whether it is inside or outside and if it is covered (e.g., by a roof, trees, or a cave). This is achieved using a simple raycast in Unreal Engine. If an item is covered, the system will consider the ground as dry, meaning that even if it rains, neither Lucy nor any dropped items will get wet. If the item or Lucy is not covered, they will get increasingly wet.
Prologue: Go Wayback! - Making a fire, sheltering from the rain
Furthermore, when items are on the ground, they absorb water more quickly, taking both water from the ground and any rain in the air. Items worn by Lucy (on the hotbar, underarm stack, in the inventory, or as clothes) will only get wet from the rain in the air (unless they are covered, in which case they will dry slowly). Staying dry becomes a matter of strategy, for instance to increase the drying process, players can move to a hot place (e.g., a shelter), get close to a fire, or if they are feeling confident expose themselves to the wind outside.
Wetness for Developers
By diving a little bit deeper (pun very much intended) into the development side of the Wetness system we can move on to discuss how the impact in the game world. We have established four different key variables that can help distinguish different types of object and dictate how they might react to exposure to water.
- WaterRetention: This internal value indicates how much water an item contains (1 means it is full, 0 means it has no water).
- Waterproofness: Determines how much water an item can absorb. For example, 0 represents a sponge, and 1 represents a rock
- Wetness: Represents how wet an item is, calculated as Retention * Absorption.
- WetValueThreshold (0.2): When the wetness value reaches this threshold, the item is considered wet. If an item’s absorption rate is below this value, it will never be considered wet. To create a waterproof item, set its absorption to a value below the WetValueThreshold.
Sweaters cycling through four stages of wetness, clockwise from top left: Dry, Damp, Soaked, Wet.
As a result we are able to test and imagine the impact of this system by ideating around some tools and scenarions we can now offer players in Go Wayback!:
- Waterproof clothes: Items with absorption rates lower than the WetValueThreshold are considered waterproof.
- Layer System: Clothing layers become wet in sequence. For instance, shoes get wet first, then socks, followed by pants, and finally the top layer. A waterproof outer layer will keep everything underneath dry when it's raining. However, this protection doesn't apply when submerged in water, as water will seep in from below. A damaged outer layer reduces the effectiveness of the layering system by allowing more water to leak through, even if the item itself doesn't become wetter.
- River wetness progression: When entering a river, clothes will gradually get wet from the bottom up. In other words, the layer system is disabled.
- Backpack wetness: Since backpacks are treated as wearable items, they can become wet or dry. Adding wet items to the backpack will make it wet, and putting dry items in a wet backpack will make them wet. A potential mechanic could allow the player to store all wet items in a backpack and dry them together, but a penalty (debug/slow drying) could be applied to prevent overly fast drying.
- Swimming with a waterproof backpack: Players can swim naked while wearing a waterproof backpack (with non-waterproof clothes inside). Upon exiting the water, the player can quickly dry their body before dressing in dry clothes.
Item drying under a roof outside.
This wetness system creates a dynamic, realistic interaction with the environment that will affect gameplay in a variety of ways. These emergent micro-stories build on the philosophy shared by Scott Davidson, our Creative Director, in our earlier article “Designing for Emergence – How Prologue Unlocks Player-Driven Journeys.”
What’s Next?
Our initial implementation for wetness is focused on the direct impact it can have on the player, but now that it is in the game we can start imagining future directions that it could grow. For instance, rainstorms could turn forest tracks into mud traps, or blizzards encase gear and backpacks in ice that, if left untended to melt, could damage electronics. As always, we are excited to hear what our community have to think of the system, and will gather feedback before iterating.
Add Prologue: Go Wayback! to your wishlist on Steam and Epic Games Store, and let us know in Discord how brutal weather should become.
About the Author
Yoan Rock is an Unreal Gameplay Programmer at PLAYERUNKNOWN Productions, where he works on systems such as wetness simulation, boarding mechanics, inventory, and UI. He has been working in the games industry since 2021 and comes from an engineering background, with experience at studios like Blacksheep Studio, Limbic Entertainment, Chillchat, and Game Atelier. Yoan mentors aspiring Unreal Engine developers in both C++ and Blueprint, and is currently developing his own courses to encourage clean, professional code with a strong engineering mindset. He also served as a technical reviewer for Beginning C++ Game Programming (Third Edition) by John Horton. In his free time, he enjoys gaming, traveling, eating cheese, and spending time with his family.
