Material Guide: Engineering Plastics for Fabrication
A comprehensive reference to the plastics most commonly used in custom fabrication — covering PET-G, HIPS, foamed PVC (Forex), HPL laminates, and coloured or specialty acrylic grades. Each profile includes mechanical properties, optical characteristics, chemical resistance, processability, and recommended applications.
Table of contents
1. PET-G (Glycol-Modified Polyethylene Terephthalate)
What is PET-G?
PET-G is a thermoplastic polyester modified with glycol to eliminate crystallisation, resulting in an amorphous, transparent material with excellent impact resistance. It is the material of choice when a project demands both optical clarity and mechanical toughness — for example, protective guards, sneeze screens, and food-contact displays.
Processing PET-G
- Laser cutting: Produces a clear but slightly rough edge. Power settings are similar to PMMA but require slightly lower speed to avoid burr formation. See Laser Cutting.
- CNC routing: Single-flute O-flute cutters work best. PET-G is somewhat gummy; compressed air cooling is recommended. See CNC Machining.
- Bending: Thermoforms well between 130–160 °C. Wider heat zone than PMMA to avoid stress whitening. See Bending & Thermoforming.
- Bonding: Does not respond to solvent cementing. Use UV adhesives or two-part epoxy/PU adhesives. See Joining Techniques.
Food contact
PET-G is approved for food contact under EU Regulation 10/2011 and FDA 21 CFR. This makes it the preferred material for gravity dispensers, bakery displays, and salad bar guards. See Standards & Certifications for compliance details.
2. HIPS (High Impact Polystyrene)
What is HIPS?
HIPS is polystyrene modified with polybutadiene rubber to improve impact resistance. It is opaque, lightweight, inexpensive, and easy to thermoform — making it a staple for packaging, signage inserts, and low-cost POS displays. HIPS is available in a wide range of solid colours as well as metallic and textured finishes.
Processing HIPS
- Laser cutting: Cuts well with CO2 laser at moderate power. Edges are matte. Produces styrene fumes — adequate extraction is essential.
- CNC routing: Very easy to machine. Use standard single- or double-flute cutters. Low melting point means slow feeds may cause melting.
- Thermoforming: Excellent thermoformability. Heat to 140–170 °C. Deep draw ratios possible. Widely used for blister packaging and trays.
- Bonding: Responds well to solvent cement (MEK or acetone). Also bonds with cyanoacrylate and hot-melt adhesives.
UV stability
HIPS has poor UV resistance and will yellow and become brittle with prolonged sun exposure. It is not suitable for outdoor applications unless UV-stabilised grades are specified or the material is painted/laminated.
3. PVC Foam (Foamed PVC / Forex)
What is foamed PVC?
Foamed PVC (commonly known by the brand name Forex) is a closed-cell, rigid PVC foam board. It is extremely lightweight, dimensionally stable, moisture-resistant, and easy to fabricate. It is the standard substrate for indoor signage, exhibition panels, and architectural mock-ups. Available in white and a range of colours, with thicknesses from 1 to 19 mm.
Processing foamed PVC
- CNC routing: The preferred method. Use single-flute upcut cutters at high RPM. Produces clean edges with minimal dust. Compression cutters prevent fraying of the foam structure.
- Laser cutting: Possible with CO2 laser but releases HCl gas. Requires acid-resistant exhaust system. Not recommended for regular production — CNC is preferred.
- Printing: Excellent substrate for direct UV flatbed printing. Smooth, matte white surface accepts ink well.
- Bonding: PVC solvent cement works well. Also bonds with cyanoacrylate, contact adhesive, and two-part acrylics.
Laser cutting caution
Laser cutting PVC releases hydrochloric acid (HCl), which is corrosive and toxic. If your facility lacks an acid-resistant exhaust and filtration system, use CNC routing instead. Many laser cutting services refuse PVC for this reason.
4. HPL (High Pressure Laminate)
What is HPL?
HPL (High Pressure Laminate) is a composite panel made by pressing multiple layers of kraft paper and decorative paper impregnated with thermosetting resins under high heat and pressure. The result is an extremely hard, scratch-resistant, and chemically resistant surface material. Commonly used for laboratory benchtops, toilet partitions, facade cladding, and high-wear furniture surfaces. Available in hundreds of colours, woodgrain, stone, and metallic finishes.
Processing HPL
- CNC routing: Requires carbide tooling due to abrasive nature. TCT (tungsten carbide tipped) or diamond-coated cutters recommended. Produces fine dust; extraction is critical.
- Laser cutting: Not recommended. HPL contains phenolic resins that produce toxic fumes and charred, discoloured edges.
- Drilling: Use brad-point or carbide drills. Pre-drill pilot holes to prevent chipping on the decorative face.
- Bonding: Contact adhesive is the standard method. Two-part epoxy for structural applications. Edge banding with matching PVC or ABS strips.
5. Coloured & Specialty Acrylic (PMMA)
Beyond clear acrylic
While standard clear PMMA is the workhorse of acrylic fabrication, specialty grades extend its capabilities into diverse applications: fluorescent acrylics for eye-catching POS displays, opal (translucent white) for LED diffusion, UV-filtering grades for museum conservation, anti-static grades for electronics, and mirror acrylic for decorative panels. Each grade has distinct processing requirements.
Fluorescent acrylic
Contains fluorescent dyes that absorb UV light and re-emit it as visible colour, creating an intensely vivid, glowing effect. The edge-lit glow is especially striking. Available in green, orange, red, pink, and blue. Laser-cuts with standard PMMA parameters. Used extensively in POS displays, signage, and art installations.
Opal (translucent white) acrylic
Diffuses light uniformly, making it the material of choice for LED lightboxes, illuminated signs, and ceiling panels. Light transmission typically 30–50%, with a Vicat softening point of 105 °C. Available as cast (better light diffusion) or extruded (lower cost).
UV-filtering acrylic
Blocks 98–99% of UV radiation below 380 nm while maintaining high visible-light transmission (90%+). Essential for museum display cases and archival framing. Meet conservation standards such as those set by the American Institute for Conservation (AIC). More expensive than standard PMMA but significantly cheaper than UV-filtering glass.
Anti-static acrylic
Treated or co-extruded with a permanent anti-static layer that prevents dust attraction and electrostatic discharge. Surface resistivity typically 109–1011 Ω. Used for clean-room windows, electronics enclosures, and museum cases where dust accumulation is problematic.
Mirror acrylic
Acrylic sheet with a vacuum-deposited metallic coating on the rear surface. Available in silver, gold, and coloured mirror finishes. Approximately 50% lighter than glass mirrors and shatter-resistant. Laser-cuts cleanly but the reflective coating may scorch if power settings are too high. Used for decorative wall panels, POS displays, and furniture accents.
6. Material Comparison Table
| Property | PMMA (cast) | PET-G | HIPS | PVC foam | HPL |
|---|---|---|---|---|---|
| Transparency | 92% (excellent) | 88–90% | Opaque | Opaque | Opaque |
| Impact resistance | Low–moderate | Very high | Moderate | Low | Moderate |
| UV resistance | Excellent | Good | Poor | Good | Excellent |
| Food contact | Yes (specific grades) | Yes | No (standard) | No | Yes (specific grades) |
| Laser cut quality | Polished edges | Good, slight burr | Matte edges | Not recommended | Not recommended |
| CNC machinability | Excellent | Good (gummy) | Excellent | Excellent | Good (abrasive) |
| Thermoformability | Good | Excellent | Excellent | Limited | Not possible |
| Solvent bondable | Yes (DCM) | No | Yes (MEK) | Yes (PVC cement) | No |
| Relative cost | Medium–high | Medium | Low | Low–medium | Medium–high |
| Density (g/cm³) | 1.19 | 1.27 | 1.04 | 0.45–0.70 | 1.35–1.45 |
7. Material Selection Guide
Choosing the right plastic depends on a combination of factors: optical requirements, mechanical loads, environmental exposure, regulatory compliance, budget, and production method. Use the decision framework below:
Quick selection rules
- Need transparency + weather resistance? → Cast PMMA
- Need transparency + impact resistance? → PET-G or polycarbonate
- Need food contact approval? → PET-G or food-grade PMMA
- Need low cost for indoor signage? → PVC foam (Forex) or HIPS
- Need extreme surface hardness? → HPL
- Need UV protection for exhibits? → UV-filtering PMMA
- Need deep thermoforming? → HIPS or PET-G
- Need flame-polished laser-cut edges? → Cast PMMA only
Common selection mistakes
Do not specify polycarbonate for laser cutting (toxic fumes, poor edge quality). Do not use standard HIPS outdoors (UV degradation). Do not assume all acrylics are food-safe (only specific certified grades). Do not use PVC foam for structural load-bearing applications (low rigidity). Always verify the material data sheet from your specific supplier, as properties vary between manufacturers.
Related articles
- CNC Machining — cutting parameters for each material
- Laser Cutting — which materials can (and cannot) be laser-cut
- Bending & Thermoforming — forming temperatures per material
- Joining Techniques — bonding compatibility matrix
- Standards & Certifications — food contact, fire ratings, compliance
- Designer’s Guide — file preparation and design rules