If you've ever printed two parts that look identical but behave completely differently — one snapping under pressure while the other bends like rubber — the answer likely comes down to one thing: Shore hardness. Understanding this single concept can completely change the way your prints perform, not just how they look.
What Is Shore Hardness?
Simply put, Shore hardness measures how hard or soft a material is. Instead of vaguely saying a material "feels soft," Shore hardness gives you an actual number on a scale, so you can make informed decisions before you ever hit print.
In resin printing, you'll commonly see values like Shore 30A, Shore 70A, or Shore 80A. But here's where a lot of people get confused — there isn't just one scale. There are two you need to know about:
- Shore A — Softer, rubbery, and flexible materials
- Shore D — Harder, more rigid, plastic-like materials
To put it in real-world terms:
| Material | Shore Hardness |
|---|---|
| Rubber band | Shore 20A – 30A |
| Car tire | Shore 70A |
| Hard hat | Shore 80D |
So when a resin is rated Shore 80A, it's flexible but still relatively firm. A rating of Shore 85D, on the other hand, means you're dealing with a very rigid plastic.
How Does This Apply to Filament?
Shore hardness isn't just a resin concept — it applies directly to FDM filament as well.
Common filaments like PLA, PETG, and ABS all fall on the Shore D scale, which is why they feel so solid and rigid. TPU, on the other hand, falls on the Shore A scale, which is what gives it that flexible, rubbery quality.
Here's a quick filament reference:
| Filament | Shore Rating | Best For |
|---|---|---|
| PLA | Shore D | Miniatures, rigid structural parts |
| PETG | Shore D | Durable rigid parts |
| ABS | Shore D | Rigid mechanical parts |
| TPU 95A | Shore 95A | Durable, semi-rigid flexible parts |
| TPU 85A | Shore 85A | Soft, rubbery flexible parts |
Why Does Shore Hardness Matter for Your Prints?
Choosing the wrong Shore hardness is one of the most common reasons prints fail or don't function as intended. If you've ever tried to print a flexible part in PLA, you already know the result — it snaps almost immediately.
Here's how to think about it:
- Low Shore A (20–50A) — Very soft and rubbery. Great for gaskets, grips, and wearable parts.
- Mid Shore A (60–80A) — Flexible but holds its shape. Ideal for functional parts that need some give, like joints or tires.
- Shore D — Rigid and strong. Perfect for miniatures, mechanical components, and structural prints.
Matching the right Shore hardness to your application is often the difference between a part that works and one that fails on first use.
A Quick Cheat Sheet
| Goal | Shore Range |
|---|---|
| Feels like rubber | Shore 20A – 50A |
| Flexible but strong | Shore 60A – 80A |
| Fully rigid | Shore D |
For filament: PLA, PETG, and ABS = Shore D / TPU = Shore A (always check the specific number).
This alone will get you 90% of the way there. The rest comes down to your individual print settings.
Shore hardness isn't just a number on a spec sheet. It determines how your print feels, how it moves, and ultimately how it functions in the real world. Whether you're printing in resin or FDM, taking a moment to check the Shore rating before you start can save you a lot of failed prints and wasted material.
Want a free copy of the Shore hardness cheat sheet?