Ampreg 31 Epoxy Wet Laminating System — Technical Details
Ampreg 31 is a low-toxicity epoxy laminating resin built for hand layup and vacuum bagging of large composite structures. Its viscosity is tuned to wet out fabric well while resisting drainage on vertical and overhead surfaces, making it a strong choice for tooling, marine hulls, and other big, complex layups. It cures to a tough, high-strength matrix at room temperature and reaches its full mechanical and thermal performance with a simple low-temperature postcure.
At a Glance (Standard Hardener)
| Mix ratio |
100:26 by weight (100:30 by volume) |
| Mixed density |
1.08 g/cm³ |
| Pot life (150 g, 25°C) |
1 hr–1 hr 10 min |
| Vacuum bagging window |
2 hr–2 hr 40 min after mixing |
| Earliest demold |
5 hours |
| Cure schedule |
Ambient cure at 18°C minimum; full properties with 16 hrs at 50°C or 5 hrs at 70°C postcure |
| Glass transition temperature (Tg) |
59°C ambient cure; up to 91°C postcured |
| Tensile strength (cured resin) |
47.6 MPa ambient; up to 78.0 MPa postcured |
| Flexural strength (cured resin) |
92.5 N/mm² ambient; up to 126.4 N/mm² postcured |
| Shelf life |
36 months when stored at 10–25°C |
Choose Your Working Time
Ampreg 31 ships with three Ampreg 3X hardener speeds, so you can match pot life to the size and complexity of the layup:
| Hardener speed |
Pot life (150 g, 25°C) |
Best for |
| Fast |
25–35 min |
Small parts, thin layups, and quick turnaround |
| Standard |
1 hr–1 hr 10 min |
General-purpose hand layup |
| Slow |
3 hr 20 min–3 hr 40 min |
Larger layups requiring more working time |
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Specialty Extra-Slow and Ultra-Slow and High Tg hardeners are also available for extended open time and elevated-temperature service, respectively. Contact us for details.
Certifications and Sustainability
- Lloyd's Register and DNV certified
- Contains 6–32% BIO-sourced carbon content as standard
- Formulated with low-toxicity hardeners and Gurit Light Reflective Technology (LRT), which fluoresces under UV light to help identify and clean up uncured resin contamination
- Tested at up to 90% relative humidity with no significant loss in interlaminar shear strength (ILSS)
Frequently Asked Questions
What is Ampreg 31 used for?
Ampreg 31 is used for hand layup and vacuum bagging of large fiberglass and carbon composite structures, including boat hulls, tooling and plugs, and other parts where good fabric wet-out and drainage resistance on vertical surfaces are important.
What is the mix ratio for Ampreg 31?
Ampreg 31 resin and Ampreg 3X hardener mix at 100:26 by weight (100:30 by volume) across the Fast, Standard, Slow, and Extra-Slow hardener speeds.
How long does Ampreg 31 take to cure?
With Standard hardener, pot life is about 1 hour and the laminate can be demolded in as little as 5 hours at room temperature. Full mechanical and thermal properties develop after a postcure of either 16 hours at 50°C or 5 hours at 70°C.
Is Ampreg 31 low-VOC or low toxicity?
Ampreg 31 uses Gurit's low-toxicity Ampreg 3X hardener range, selected to improve health and safety compared with older-generation hardeners. Standard epoxy PPE, including nitrile gloves, eye protection, and adequate ventilation, is still required. See the full Safety Data Sheet before use.
What is the difference between Ampreg 31 and Ampreg 30?
Both are low-toxicity Gurit epoxy laminating systems with the same 100:26 mix ratio and hardener speed lineup. Ampreg 30 has a lower initial mixed viscosity, making it easier to wet out heavyweight reinforcements. Ampreg 31 is viscosity-optimized to balance good wet-out with drainage resistance, making it better suited to vertical and overhead surfaces.
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