Polycarbonate vs Acrylic Tube: Impact, Clarity, Temperature and Cost

Two clear tubes, two different compromises

Polycarbonate and acrylic are the two transparent thermoplastics that get extruded into tube, and from a metre away they look identical. Up close they are opposites: acrylic is the clearer and more scratch-resistant of the two and shatters; polycarbonate is nearly unbreakable and yellows in sunlight.

Choosing between them is therefore not a matter of "which is better" but of which failure mode the application can tolerate. A machine guard that cracks is a safety incident. A display tube that has yellowed is a cosmetic complaint. Those are different risks and they point at different materials.

Optical: transmittance, haze and edge colour

Acrylic is the clearer material, and the difference is visible on thick sections even though the datasheet numbers look close.

Table 1 — Optical comparison. The transmission difference is small; the difference in edge appearance and long-term yellowing is not.

The edge is where acrylic wins visibly. Its higher clarity and lower refractive index make a cut or polished edge glow with light, which is why acrylic tube is used for light guides and illuminated displays. Polycarbonate edges look duller and slightly green by comparison, because of the slight inherent tint in the resin.

Scratch resistance matters more than the datasheet suggests. Polycarbonate scratches at pencil hardness HB and every handling mark shows under light. Acrylic sits around 2H and survives cleaning. Where the tube will be wiped, handled or cleaned regularly, either specify a hard-coated polycarbonate or accept acrylic.

Impact: the number that decides most projects

This is the real difference and it is not marginal. Polycarbonate is roughly thirty to fifty times tougher than acrylic in notched impact, and the failure modes are qualitatively different.

Table 2 — Impact comparison. The notched Izod figures differ by a factor of thirty; the practical difference is that one dents and the other breaks.

Polycarbonate's toughness is not unconditional. It is notch sensitive: a sharp scratch, a machined corner without a radius, or a solvent-induced craze becomes a crack initiation site and the tube fails at a fraction of its rated impact. A polycarbonate tube with a sharp machined groove can be weaker than a plain acrylic tube.

That is why the machining rules matter. Every cut edge should be deburred and every internal corner radiused. A polycarbonate guard that has been drilled with a blunt bit and left with a ragged hole will crack from that hole, and the material will be blamed.

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Table 3 — Thermal comparison. Polycarbonate buys roughly 40 °C of extra service temperature, which is decisive for anything near a heat source.

Both materials expand about seven times as much as steel, and a 2 m tube moves 2.6–2.8 mm over a 20 °C swing. Any installation that clamps both ends rigidly will either bow the tube or crack it, whichever material is used. One end should always be free to slide.

The 40 °C difference in service temperature decides a lot of industrial applications. A guard over a motor, a sight glass on a warm process line, a light cover near a lamp — all of those push acrylic past its limit and leave polycarbonate comfortable.

Chemical resistance

Neither material is chemically inert, and they fail to different things. This is the section where a wrong choice produces a part that fails in a month.

Table 4 — Chemical resistance. Polycarbonate's weakness is stress cracking at low chemical exposure; acrylic's is dissolution at higher exposure.

The polycarbonate failure mode is the more insidious. It does not need to be immersed — a wipe with an alcohol-based cleaner on a part that is under assembly stress will craze it, and the crazing turns into cracks over weeks. This is why the cleaning agent matters as much as the process fluid: specify a mild soap solution, never a solvent wipe.

Acrylic's failure is more obvious. It softens, frosts or dissolves, and the change is visible immediately. In that sense acrylic is the more forgiving material to specify, because the mistake announces itself.

Machining and forming

Table 5 — Machining comparison. Acrylic is the easier material to finish; polycarbonate is the easier one to bend without breaking.

Both need drying before thermoforming. Polycarbonate absorbs up to 0.35% moisture and will show bubbles and haze if formed wet; acrylic absorbs less but still needs 2–4 hours at 80 °C. This is the single most common cause of a failed forming trial on either material.

Laser cutting is a clear win for acrylic. A CO₂ laser produces a flame-polished edge that needs no further work, and the cut is clean on thicknesses up to 20 mm. Polycarbonate cuts but the edge discolours and the material is prone to micro-cracking along the cut, so a protective film and a nitrogen assist are usually needed.

UV and weathering

Acrylic is inherently UV stable. It does not need an additive, it does not yellow meaningfully over a decade outdoors, and it does not embrittle. This is why it dominates signage and architectural glazing.

Polycarbonate is the opposite. Standard grades yellow within two to three years outdoors, and the yellowing is accompanied by embrittlement — the surface degrades and the impact strength that justified the material drops away. A UV-stabilised grade slows this; a coextruded UV cap layer is better and is what most outdoor polycarbonate sheet uses.

For a tube, a coextruded cap is difficult, so the practical options are a UV-stabilised compound or a hard coat that also carries UV absorbers. Either way, if the application is outdoors, specify the UV protection explicitly and ask for a weathering data sheet — the base resin grade alone does not tell you.

Cost and specification

Table 6 — Cost comparison. The material premium for polycarbonate is 1.6–2.5×, and the UV and coating requirements widen it further.

When specifying either, five things belong on the drawing: outside diameter and tolerance, wall thickness and tolerance, length and tolerance, the grade (including UV or hard coat), and the end finish. "Clear tube" is not a specification, and the difference between an as-extruded end and a polished end is a visible cost.

Concentricity is the item most often left off. A tube with 0.3 mm of eccentricity will look fine until it is used as a bearing surface or a sight glass, at which point the optical distortion becomes obvious. Specify concentricity, not just wall thickness.