Seven transparent sheet materials, compared on the numbers that matter

1. Optical and physical

What you see and how much punishment it takes.

Material	Light transmission	Impact resistance	Scratch resistance	Max service temp.
Cast acrylic (PMMA)	92%	Low — brittle, cracks	Good	70–80 °C
Extruded acrylic	92%	Low — slightly more brittle than cast	Good	65–75 °C
Polycarbonate (PC)	88–90%	Very high — ~200× acrylic	Poor without hard coat	115–125 °C
Polystyrene (PS)	88–90%	Low — very brittle	Poor	65–75 °C
PETG	85–88%	Medium-high — tough, deforms rather than cracks	Fair	65–70 °C
Clear rigid PVC	80–85%	Medium	Fair	55–60 °C
Soda-lime glass	90–91%	Very low — shatters	Excellent	150 °C+

2. Durability and chemical resistance

How each one ages, and what attacks it.

Material	UV / yellowing	Alcohol resistance	Solvent resistance	Typical outdoor life
Cast acrylic	Yellows gradually; UV grade extends it	Good — survives wipe-down	Poor — acetone and MEK attack it	3–5 years with UV grade
Extruded acrylic	Similar to cast, slightly faster	Good	Poor, and stress-cracks more readily	2–4 years
Polycarbonate	Yellows notably within 2–3 years unless UV-coated	Fair — repeated exposure clouds it	Attacked by ketones and chlorinated solvents	2–5 years with UV coat
Polystyrene	Yellows quickly	Poor — crazes	Very poor	Not recommended
PETG	Good; less yellowing than PS	Good	Fair — better than acrylic	2–3 years
Clear rigid PVC	Good, but discolours with heat	Good	Fair	3–5 years
Glass	None	Excellent	Excellent	Indefinite

3. Machinability and joining

Whether we can cut, bend, polish and bond it — this is where most material decisions actually get made.

Material	Machining	Heat bending	Solvent bonding	Polishing
Cast acrylic	Excellent — clean chips, holds tolerance	Excellent, 150–170 °C	Excellent — near-invisible joints	Excellent — diamond or flame
Extruded acrylic	Good, but stress-cracks around holes	Good, narrower window	Fair — joints show more	Fair
Polycarbonate	Good — needs sharp tools, tends to melt	Possible but difficult, needs drying	Poor — solvent bonding unreliable	Fair — hard to get optical finish
Polystyrene	Fair — chips easily	Good	Good	Fair
PETG	Fair — gummy, clogs tools	Good	Fair	Poor — does not polish clear
Clear rigid PVC	Good	Fair — narrow window	Good with specific solvents	Fair
Glass	Not applicable — cut and edge-ground only	Not possible	UV adhesive only	Factory edge only

4. Cost and one-line verdict

Material	Relative cost	Use it when
Cast acrylic	Baseline	You need clarity plus machined or bent geometry. This is the default for 80% of our work.
Extruded acrylic	10–20% cheaper	Flat, unpolished parts where nobody inspects the edge and cost is the driver.
Polycarbonate	2–3× acrylic	Something is going to hit it. Guards facing swarf, machine windows, vandal-prone panels.
Polystyrene	20–30% cheaper	Indoor display where cost dominates and life is short. Rarely worth the savings.
PETG	1.2–1.5× acrylic	You need toughness plus solvent resistance and do not need optical clarity.
Clear rigid PVC	1.1–1.4× acrylic	Chemical environments, or where fire rating matters. Not for optical work.
Glass	Varies widely	Scratch resistance, heat, or permanence outweigh weight and breakage risk.

Thirty-second selection

If the part is…	Use
A retail display, machined and polished	Cast acrylic
A flat sign or panel, cost-sensitive	Extruded acrylic
A guard facing flying debris	Polycarbonate
Bent and bonded into a shape	Cast acrylic, annealed if thick
Cleaned with aggressive solvents	PETG or clear PVC — not acrylic
Autoclaved or exposed above 90 °C	Glass or a high-temperature engineering plastic
Outdoors for more than five years	UV-stabilised acrylic, or glass
Scratch resistance is the priority	Glass, or hard-coated polycarbonate

What can be swapped, and what cannot

Generally safe swaps: cast for extruded on flat unpolished work (cheaper, slightly worse edge); PETG for acrylic where optical clarity is not critical and toughness is.

Swaps that usually fail: polycarbonate in place of acrylic where you need polished optical edges — it does not polish clear. Acrylic in place of polycarbonate in an impact application — it will crack. Glass in place of acrylic where weight or breakage is the reason you chose plastic.

If you are substituting a material on an existing approved design, tell us what the original was and why you are changing it. The failure mode is usually in the reason for the change, not in the new material.