Special Offer: Get free Stashnote stickers with every order!

10% OFF with code “WelcomeCWnew”

CacheWerk - Your Geocaching & Outdoor Shop

Free shipping on orders over €25! (EU only)

TPU Buffer on the Geocache: Function, Pressure, and Limits

by Benedikt
TPU-Puffer am Geocache: Funktion, Druck und Grenzen - CacheWerk

A TPU buffer is the flexible intermediate piece in a geocache. It clamps a PETling in place in a tube, dampens shocks, prevents rattling, or seals a lid. TPU is suitable for this because it gives like rubber and then returns to its shape. But it is no miracle material. Here you will read what a TPU buffer is worth, which hardness and printing settings are suitable, and where its limits lie, so that the logbook is still dry after the third winter.

Cachewerk
Suitable hides for your cache idea
Cachewerk offers creative geocaching hides, camouflage, and 3D-printed special items for individual solutions around your cache.

The most important things in brief

  • A TPU buffer is not a container, but a functional part: It clamps, dampens, holds, or seals. For the container itself, a rigid material like PETG is usually the better choice.
  • Shore 95A is the standard for buffers and seals: This hardness is easy to print and deforms less under pressure than soft 70A TPU.
  • Print slowly, warm, and dry: around 210 to 240 °C, 15 to 30 mm/s, little fan, and pre-dried filament.
  • Printed seals are unreliable: If it really needs to be tight, a purchased O-ring is the safer solution. The TPU buffer then takes over the clamping and dampening.
  • Pay attention to the rules: For other physical caches, a minimum distance of 161 m applies, and a cache may not be buried.

Table of Contents

What a TPU buffer does at the geocache

“TPU buffer” is not a fixed technical term from the geocaching guidelines. In the maker scene, it almost always means a printed part made of thermoplastic polyurethane that sits between two solid parts and gives there. TPU is elastic, abrasion-resistant, and withstands frequent bending. That is exactly why it is used in 3D printing for seals, shock absorbers, and buffers.

At the cache, five forms appear above all:

  • Clamping buffer: a ring or sleeve that holds a PETling or a small tube in a tube, a post, or a hole. The soft material compensates for small dimensional deviations without the container falling out.
  • Sealing buffer: a flat disc or ring under the lid that is intended to fill the gap between the lid and the container.
  • Shock and rattle protection: a cushion that prevents a container from rattling audibly in the hide or hitting metal when taken out. A rattling hide quickly gives itself away, even to muggles.
  • Hanger: flexible holders on which a PETling hangs in a tree or bush. There are even ready-made print files for this, such as a TPU hanger for PETlings in tree caches.
  • Magnet buffer: a thin intermediate layer between the magnet and the metal surface. It protects the paint and surface and ensures that the cache does not slip.

The container itself remains the main thing. A traditional needs at least a container and a logbook. The buffer only ensures that both stay in place and work as long as possible.

TPU, PETG or rigid container material?

Many owners wonder if they should print the entire cache out of TPU. Usually the answer is: no. TPU is elastic, rubbery, and shock-absorbing, PETG on the other hand tough and only slightly flexible. Furthermore, TPU is more demanding and slower to print. A container must be dimensionally stable so that threads and lids fit. A buffer should do exactly the opposite: give.

Criterion TPU (Shore 95A) PETG Ready-made plastic container (e.g. PETling)
Behavior rubbery, springs back tough, dimensionally stable, slightly flexible rigid
Typical role at the cache Buffer, clamping ring, shock absorber, hanger Housing, camouflage, holder, caps actual logbook container
Printing effort high: slow, dry, preferably Direct Drive medium not applicable
Sealing effect only as a supplement, unreliable when printed via threads and seal factory-sealed with seal
Good for Clamping, dampening, compensating tolerances visible parts that must remain stable outside dry logbook

The most sensible combination therefore looks like this: a rigid housing made of PETG or a ready-made PETling as the actual container, plus a small TPU part at the place where something needs to clamp or dampen.

The right hardness and TPU type

TPU is sold by Shore hardness. The lower the value, the softer the material. For geocache buffers, 95A has established itself, and for good reason.

The chemical type also plays a role. Polyether TPU is considered hydrolysis- and microbe-resistant and is chosen for parts in water and outdoors. Aromatic TPU types yellow under light, aliphatic are light-resistant. Unfortunately, many filament spools do not state which type is inside. Then only the manufacturer's data sheet or your own test in the garden helps before the buffer gets to a real cache.

Printing TPU buffers: Settings that work

TPU is less forgiving than PLA or PETG. Because the filament is soft, it can bunch up in the extruder. A Direct-Drive extruder is particularly suitable for flexible TPU. With a Bowden extruder, firmer 95A still works, while very soft TPU becomes difficult.

These guidelines are a good starting point:

Setting Guideline
Printing temperature 210–240 °C
Bed temperature 30–60 °C
Printing speed 15–30 mm/s
Part fan 30–50 %
Retract 0.5–1.5 mm or initially off completely

Temperature, bed, speed and fan come from the overview by 3D-Druck-Archiv. It also states there that too strong cooling worsens layer adhesion. The Anycubic wiki on TPU printing gives slightly tighter values for TPU from 95A: 220–230 °C, 20–30 mm/s and 0.5–1.5 mm retract or no retract initially.

This is how you proceed step by step:

  1. Dry the filament. TPU absorbs a lot of moisture. According to Anycubic, wet material leads to bubbles, rough surfaces and poor layer adhesion. For a buffer that needs to sit tight, a rough surface is a real problem.
  2. Start slowly. Print the first buffer at the lower end of the speed range. You can speed up later.
  3. Turn down the fan. Better a little less cooling and instead layers that adhere well to each other.
  4. Keep retract minimal. A lot of retraction bunches up the soft filament. Stringing is normal with TPU and can be easily removed afterwards.
  5. Test print in the real hide. Print two or three variants with slightly different dimensions and try them out on the tube or post before you decide.

Construction: How the buffer sits correctly

A good buffer starts in CAD, not at the printer. A few principles help:

  • Work with oversize, but in moderation. A clamping ring should be slightly larger than the opening so that it sits under tension. Too much oversize means: The finder cannot get the container out or tears the buffer off when pulling.
  • More walls instead of much infill. For TPU parts, multiple perimeters ensure uniform springback. A buffer made of almost pure walls springs back more predictably than one with a lot of infill.
  • Grooves or ribs instead of a smooth wall. A clamping buffer with circumferential ribs holds better in the tube and compensates for unevenness. You know this from wall plugs.
  • Plan a grip for the finder. A small tab or ring on the buffer helps with pulling it out. Without a tab, the cache quickly becomes a case for the pliers, and that damages the hide.
  • Separate the buffer and container. If the buffer is its own part, it can be easily replaced during maintenance without having to print the entire cache again.

Also think about what the buffer has to withstand in everyday use: dozens of finders who pull sometimes carefully and sometimes roughly. A buffer that tears on the first winter deployment will bring you DNF logs and maintenance trips. More about materials that stay outside permanently, read in our guide to extremely robust geocache containers.

How tight does a cache become with a TPU seal?

Here comes the honest answer that many do not want to hear: A printed TPU seal is no guarantee for a dry logbook. In a test by Prusa Research the tested 3D-printed seals did not hold tight, O-rings were the most reliable. Decisive there were many wall lines and a very smooth surface exactly at the place where the seal rests. At higher water pressure, every printed solution reaches its limits.

For practice, this means:

  • Keep the sealing surface smooth. The contact surface on the container should be as flat as possible. Every layer groove is a small channel for water.
  • O-ring for the seal, TPU for the rest. Design a groove for a commercially available O-ring and use TPU where it has its strengths: clamping and dampening.
  • Protect the logbook additionally. A small zip bag or a weatherproof logbook is the cheapest insurance.

Even with small nano containers made of TPU, the question remains open. For a magnetic nano logbook container made of TPU, the creator writes that the unlosable cap closes well, whether it is rainproof was still unclear. How you reliably keep small cans dry, we show in the instructions Sealing a nano can.

By the way, the same logic applies to everything that sticks on the outside of the cache: A label with the cache name and a hint for muggles only holds if the material and surface match. What matters for waterproof vinyl stickers for outdoors can be well transferred to labeled geocache containers.

Weather, UV and frost: What TPU withstands outside

A geocache container should according to be waterproof and withstand extreme temperature fluctuations. How does TPU fare with this?

Frost: TPU remains elastic even in the cold. This is a real advantage over many other plastics that become brittle in winter. A clamping buffer in the post tube therefore also holds in January.

Heat: A post in the sun or a dark shield can get really hot in summer. The material supplier dicht.de calls a heat resistance of 74 °C for TPU 95A and lists UV and high moisture absorption as weaknesses. More important than the peak temperature is however the continuous pressure: Under continuous compression, especially in heat, TPU gives more than vulcanized elastomers. A buffer that was squeezed together for two summers often clamps less firmly afterwards.

UV: Who builds the buffer visibly should expect yellowing and aging, especially with aromatic TPU. It is best to build the buffer so that it sits in the shade or inside the hide.

Maintenance: Check the buffer at every maintenance visit. If the container sits looser than before, a new buffer can be printed quickly. Plan that from the beginning. More tips for permanent hides can be found in the Tutorial on the weatherproof cache hide.

TPU Limits and Maintenance Outdoors

Before Hiding: Size, Distance, and Permission

The best buffer is useless if the cache is not published. Three points you should clarify beforehand:

Size: The usual classification includes Nano (usually under 10 ml), Micro (under 0.1 l), Small (0.1 to 1 l), Normal (1 to 20 l), and Large (over 20 l). TPU buffers are usually used for Nanos and Micros, such as PETlings in posts or pipes. Ideas for the smallest containers can be found under Hiding Nanos.

Distance: According to the Geocaching HQ Geocache Guidelines, a minimum distance of 161 m (0.1 miles) applies between containers and physical stations of different caches. Do not rely solely on the planning map, as multis, mysteries, wherigos, and letterbox hybrids may have hidden physical waypoints. How to properly check a location is shown in our Guide to Scouting a Cache Location.

Permission and Placement: For every cache, you need the permission of the owner or the responsible authority. Burying is taboo. Why this is the case, we explain under Burying Geocaches. A TPU buffer should therefore never be used to anchor a container in the ground. For inconspicuous mounting in the cityscape, our Workflow for Inconspicuous Cache Placement helps.

Our View from the Cacher Workshop

We are active geocachers ourselves and develop our hides the way we need them outdoors. For the load-bearing parts, we print in PETG: housings, caps, camouflage, and holders must remain dimensionally stable so that threads and fits still work after months in the rain. We see TPU as a specialist for a single task, namely to give way.

Our experience from many hide ideas: The problems with owner caches rarely arise from the rigid housing, but from the transitions. The container wobbles in the pipe, the lid lets moisture through, or the hide rattles. That is exactly where a small TPU buffer can make a big difference. But anyone who tries to solve everything with TPU at once, i.e., housing, seal, and holder in one, usually ends up with a cache that is neither properly sealed nor properly stable.

Our advice: Separate the tasks. A proven container for the logbook, a dimensionally stable housing for camouflage and support, and TPU only where it needs to clamp or dampen. This makes your cache low-maintenance, and your finders will enjoy a hide that still works after two years just like on the first day.

Finished Hides Instead of Printing Experiments

Would you rather hide a cache right away instead of first testing shore hardness and retraction values? Then take a look at our shop. Our 3D-printed Geocaching Hides and Wooden Hides are developed by cachers for cachers and tested for outdoor use. For pipe posts, there is, for example, our Bundle with Two 60 mm Post Caps with PETlings: weatherproof, inconspicuous, and ready to use immediately. For the city, the magnetic Screw Hide with Secret Compartment is ideal. And if you still want to print yourself, you will find suitable 3D Printing Files for Geocaching with us.

Bundle 2x Geocaching Post Cap 60mm – Camouflaged Hide with PETlings | Weatherproof & Inconspicuous

Frequently Asked Questions

Can I print an entire Geocache container out of TPU?

It is possible, but usually not practical. TPU is soft, so threads and lids fit less precisely, and printing takes longer. Better is a rigid housing made of PETG or a finished PETling, combined with a TPU buffer at the point that needs to give way.

Which Shore hardness is suitable for a TPU buffer?

For most buffers, clamping rings, and sealing washers, 95A is the right choice. This hardness can also be processed with many standard printers and deforms less under pressure than soft TPU. Softer material dampens more, but gives in faster under continuous pressure.

Does a printed TPU seal keep my logbook dry?

You should not rely on it. In tests, printed seals were less reliable than commercially available O-rings. It is better to plan an O-ring groove and additionally protect the logbook with a small bag.

How often should I replace a TPU buffer on a cache?

There is no fixed period, because sun, heat, and the number of finds play a role. Check the buffer during every maintenance: If the container is noticeably looser or the material has cracks, print a new one. Designed as a separate part, replacement is done in a few minutes.

Sources

Recommendations

by Benedikt