The steel you choose for your injection mold determines how long it lasts, how well it performs, and how much it costs — both upfront and over the life of production. P20 and H13 are the two most common tool steels used in injection mold manufacturing, and they serve very different purposes. Choosing the wrong one can cost you tens of thousands of dollars in premature wear, unexpected repairs, or over-engineered tooling you didn't need.
At Ace's Injection Molding in Bohemia, NY, we build molds in both materials regularly. Here's an honest, technical comparison to help you understand when each steel makes sense — and when it doesn't.
Why Mold Steel Selection Matters
An injection mold operates under extreme conditions. Every cycle, molten plastic at 400–700°F is injected under pressures exceeding 10,000 PSI, held against steel cavity surfaces, then cooled and ejected. A production mold might repeat this cycle every 20–45 seconds, hundreds of thousands of times per year.
The steel has to withstand this thermal cycling, resist wear from abrasive fillers in the resin, maintain dimensional accuracy over hundreds of thousands of shots, and accept a polish or texture that transfers consistently to every part. Choosing the right steel for these demands isn't a guess — it's an engineering decision based on your resin, your volume, and your quality requirements.
What Is P20 Steel?
P20 is a pre-hardened chromium-molybdenum alloy tool steel. It arrives from the supplier already heat-treated to 28–34 HRC (Rockwell C hardness), which means it can be machined, polished, and put into service without additional heat treatment. This is one of its biggest practical advantages — it simplifies the mold building process and reduces lead time.
P20 offers good machinability, decent wear resistance, and accepts a polish up to SPI A-2 level (high gloss). It's readily available, relatively affordable, and has been the workhorse of the injection mold industry for decades. Most general-purpose production molds running commodity resins like ABS, polypropylene, polycarbonate, or nylon (unfilled) are built from P20.
Typical mold life for P20: 500,000 to 1,000,000+ shots depending on resin and part geometry.
What Is H13 Steel?
H13 is a hot-work tool steel — a chromium-molybdenum-vanadium alloy designed specifically for high-temperature applications. Unlike P20, H13 is supplied in an annealed (soft) state and requires heat treatment after machining to achieve its working hardness of 48–52 HRC. This heat treatment step adds time and cost to the mold build, but the resulting properties are significantly superior for demanding applications.
H13 excels in three areas: heat resistance, wear resistance, and toughness at elevated temperatures. It maintains its hardness and dimensional stability at operating temperatures that would soften P20. It resists abrasive wear from glass-filled, mineral-filled, and carbon-fiber-filled resins far better than P20. And it handles the thermal shock of repeated heating and cooling cycles without checking (surface cracking).
Typical mold life for H13: 1,000,000+ shots, often exceeding 2,000,000 with proper maintenance.
P20 vs H13 — Side-by-Side Comparison
- Hardness: P20 at 28–34 HRC vs H13 at 48–52 HRC (after heat treatment). H13 is significantly harder, which translates to better wear resistance but more difficult machining.
- Heat Treatment: P20 comes pre-hardened — machine it and go. H13 requires hardening and tempering after machining, adding 1–2 weeks and cost to the mold build.
- Machinability: P20 machines easily with standard carbide tooling. H13 in its annealed state machines reasonably well, but any post-heat-treatment modifications require hard milling or EDM.
- Wear Resistance: P20 handles unfilled and lightly filled resins well. H13 is the choice for glass-filled nylons, PPS, PEEK, and other abrasive or high-temperature resins that would erode P20 prematurely.
- Polishability: Both steels polish well. P20 achieves SPI A-2 comfortably. H13 can reach SPI A-1 (mirror finish) due to its finer grain structure at higher hardness.
- Cost: P20 is less expensive — both in raw material and in mold building time (no heat treatment step). H13 typically adds 15–30% to the tooling cost depending on mold complexity.
- Mold Life: P20 delivers 500K–1M shots. H13 delivers 1M–2M+ shots. For very high-volume programs, H13's longer life offsets its higher upfront cost.
When to Choose P20
P20 is the right choice for the majority of injection mold applications. Choose P20 when:
- Your production volume is under 500,000 parts over the life of the tool
- You're running unfilled commodity resins — ABS, PP, PE, PS, PC, acetal, or unfilled nylon
- Lead time is a priority and you can't afford the extra weeks for heat treatment
- Your part doesn't require extreme surface finishes (SPI A-1 mirror polish)
- Budget is a constraint and the mold needs to be cost-effective for the program volume
P20 is not a compromise — it's the appropriate engineering choice for most production scenarios. Over-specifying H13 when P20 would do the job wastes money without delivering meaningful benefit. For a full cost breakdown of tooling and per-part pricing, see our injection molding cost guide.
When to Choose H13
H13 earns its premium in applications where P20 would fail prematurely or deliver inconsistent results. Choose H13 when:
- You're molding glass-filled, mineral-filled, or carbon-fiber-filled resins that abrade softer steels
- The resin requires high melt temperatures — PPS, PEEK, PEI (Ultem), or liquid crystal polymers (LCP)
- Production volume exceeds 1,000,000 shots and you need the mold to last
- The part requires SPI A-1 mirror polish that must be maintained over long production runs
- You need hot runner valve gate systems where steel hardness at the gate area is critical
- Tight tolerances must be held consistently over very long runs without dimensional drift
In these scenarios, H13's higher cost is an investment that pays back through longer mold life, fewer repairs, and more consistent parts over the production run.
What About Aluminum Molds?
Not every project needs steel at all. For prototype runs, design validation, bridge production, or volumes under 100,000 shots, aluminum molds (typically 7075 or 6061 alloy) offer significant advantages: faster machining, lower cost, and lead times as short as 2–4 weeks.
Aluminum won't match steel for longevity or wear resistance, but for the right applications, it's the smartest choice. At our Long Island mold shop, we build a lot of aluminum prototype tooling for customers who need parts fast for testing, trade shows, or market validation — then transition to steel production tooling once the design is locked in. Read more about when low volume injection molding makes sense.
The key is matching the mold material to the actual production need, not defaulting to the most expensive option.
How Aces Chooses the Right Material
When you bring a project to Ace's Injection Molding in Bohemia, NY, we don't default to one material. We evaluate your specific requirements:
- What resin are you running? Unfilled nylon is very different from 30% glass-filled nylon when it comes to mold wear.
- What's your expected lifetime volume? 50,000 parts and 5,000,000 parts demand different tooling strategies.
- What surface finish does the part require? Cosmetic A-surfaces behave differently than hidden structural parts.
- What's your timeline? If you need parts in 4 weeks, we're not recommending H13 with an 8-week mold build.
- What's your budget reality? We'll tell you honestly when P20 is the right call and when spending more on H13 actually saves money long-term.
This isn't a sales conversation — it's an engineering conversation. We've been making molds on Long Island for over three decades, and we've seen what happens when the wrong steel meets the wrong application. Our job is to make sure that doesn't happen to your project.
Other Tool Steel Options Worth Knowing
P20 and H13 cover the vast majority of injection mold applications, but they're not the only options. Depending on your requirements, these steels may also come up:
- 420 Stainless Steel: Used when corrosion resistance is critical — medical devices, food-contact parts, or molds running PVC or flame-retardant resins that outgas corrosive byproducts. Harder to machine than P20, but essential when chemical attack is a concern.
- S7 Tool Steel: An impact-resistant shock steel sometimes used for mold components that take heavy ejection force or unsupported shut-off sections. Not common for full cavity/core construction but useful for specific mold components.
- 7075 and 6061 Aluminum: Not steel at all, but worth mentioning. Aluminum tooling is the right call for prototype and bridge production under 100,000 shots. It machines at 3–5x the speed of steel and costs a fraction of a P20 mold. For getting parts fast and validating your design before committing to production steel, aluminum prototype tooling is hard to beat.
- Beryllium Copper (BeCu): Occasionally used for cores or inserts in areas with difficult cooling requirements. BeCu has exceptional thermal conductivity — 2–3x better than steel — which accelerates cooling in features like thin cores or deep ribs. It's expensive and requires careful machining practices, but in the right application it dramatically reduces cycle time.
Frequently Asked Questions About Mold Steel
Can I change the steel after the mold is built?
Not really. The mold is designed and machined to specific dimensions. If you need to replace cavity or core inserts, they can be remade in a different material, but it's a significant cost. Getting the material right upfront is the only practical approach.
Does Google know what steel my mold is made of?
No — and neither does your customer. What they know is whether parts are consistent, whether the mold ran reliably for 800,000 shots, and whether it held tolerance. The steel is a means to an end. Choose based on your production needs, not perception.
My overseas quote specifies "718 steel" or "NAK80" — how do those compare?
718 is a Chinese pre-hardened mold steel roughly equivalent to P20. NAK80 is a Japanese pre-hardened steel with slightly better polishability than standard P20. Both are legitimate materials used in international tooling. The quality concern with offshore tooling isn't usually the raw steel — it's the machining quality, tolerances, and what happens when you need a modification.
How do I know if my current mold is P20 or H13?
If you have the mold build documentation, it should be specified. If not, a hardness test on a non-critical surface (Rockwell C tester) will tell you: 28–34 HRC suggests P20 or equivalent, 48–52 HRC suggests H13. We can check this for any mold that comes through our shop.
If you're planning an injection mold and want straight advice on materials, tooling approach, and realistic costs, reach out. We'll review your part and give you a recommendation you can trust. For a step-by-step look at the full mold building process, read how injection molds are made. Planning your timeline? See our lead times guide.
Need Help Choosing Mold Steel?
Send us your part design and production requirements. We'll recommend the right tooling material and provide a detailed quote — no pressure, no upsell.