Acrylic or polycarbonate — how to choose, and what the comparison charts do not tell you

The quick answer, for people in a hurry

If the part can be struck, stood on, or lives outdoors in a demanding location, the answer is PC. Otherwise, acrylic is usually the right answer — it is clearer, harder and cheaper. That table answers most of the enquiries we get. Everything below is the part the table cannot show.

The same die, two different parts

Run a round-tube die in acrylic, then run the same die in polycarbonate, and the part is not the same size. On the outside diameter, the PC comes out roughly 0.4–0.5 % smaller than the acrylic from the same tooling, because PC shrinks more as it leaves the die and cools.

That sounds like a rounding error and it is not. Half a per cent on a 100 mm tube is half a millimetre — enough to fail a fit that was designed around the acrylic number. A material swap is never just a material swap. It is a re-calibration, and a drawing dimensioned for one material does not carry over to the other for free.

Surface and light: the number is not the whole story

PMMA transmits roughly 92 % of visible light and PC roughly 88–89 %, and those are typical resin figures, so the difference is real but small. What the datasheet misses is the surface. PC is softer, and as it comes out of the die it does not have the same glassy finish as acrylic, which scatters a little light on top of the material's own figure. The same softness is why PC shows handling and cleaning scratches sooner than acrylic does.

There is a process difference hiding behind this, and it is one of the places we have spent the most effort. PC tends to leave fine drag lines on the surface as it is drawn through the calibrator. Our newer PC process cuts those drag lines dramatically — worth saying plainly, because it is the difference between a PC part that reads as "plastic" and one that reads as "glass".

Impact: where the two stop being comparable

Acrylic is a rigid, glass-like material — strike it hard and it shatters. PC is ductile — it deforms and springs back. The standard impact-protection rating, IK, puts a number on it: acrylic generally reaches IK06–IK07, while PC clears IK10 without difficulty. That is not a small gap. IK10 is the level specified for enclosures that are expected to take a hard knock. If the part can be struck or stood on, this one line usually settles it.

Heat: the twenty degrees that decide

Heat follows the same shape. Acrylic is comfortable to roughly 100 °C and PC to roughly 120 °C in service — the exact figure moves with the grade and the load, but the gap is consistent. Anything that sits near a lamp, inside an engine bay, in a sealed enclosure in summer sun, or on a machine that runs warm is where those twenty degrees are the whole decision.

Ageing: the part most charts leave vague

This is where we can be specific, including the part that is inconvenient.

Clear acrylic lets more than 90 % of ultraviolet light straight through it. Worth knowing before you buy acrylic as a "UV guard", because it is not one — the UV passes through and reaches whatever is behind the sheet. What acrylic does well is hold up to that UV itself; it is the most weather-stable of the clear plastics.

PC is the other way round: UV affects it more, and over time it yellows. The usual story stops there, which is a shame, because the reason is simple and it changes how you read the problem. The monomer PC is built from — BPA — is itself faintly yellow. Resin makers add a colour correction during production so the finished material reads as clear. Over years outdoors that correction fades before the polymer does, and the yellow that was underneath all along begins to show. What people call "PC yellowing" is, more often than they think, a colour correction fading — not the material suddenly turning on you.

We put numbers on it where we can. A conventional UV-stabilised PC from us generally stays within a colour difference of ΔE 2 over two years outdoors; if you need a ten-year weatherable PC, that is a different compound and we can supply it. And to be clear about the baseline: every PC and every acrylic we run carries anti-ageing and anti-UV additives — it is not a priced option you have to remember to ask for.

On resin choice we do not play favourites between the majors. Different grades have different strengths, and we pick the one that fits your requirement — the temperature, the UV duty and the market — rather than the one we happen to have on the floor.

Flame: the quiet deciding factor

PC is inherently far harder to ignite than acrylic and can be supplied flame-retardant; acrylic burns readily. If a flammability rating is part of your specification, say so early — it usually pushes the answer towards PC, and sometimes towards a specific compound, before we get to anything else.

Bonding and machining: what we tell customers

Both materials bond, but they reward different care. Acrylic solvent-bonds cleanly — and this is where our annealing earns its keep, because the residual stress annealing removes is exactly the stress that turns a solvent bond silver and cracked. PC bonding is more demanding: the two things that move the cracking risk most are the ambient temperature and humidity at the joint, not the brand of adhesive. A cold, damp morning behaves differently from a warm, dry afternoon, and a joint made in the wrong conditions can look perfect and fail later.

Drilling is the other place people blame the material when the problem is the process. A crack running out from a drilled hole is not really "PC being brittle" or "acrylic being brittle" — it is heat. The drill heats the wall, the part cools, and that cycle stacks stress exactly around the hole. Control the cooling while you drill, and treat the hole afterwards, and the risk drops sharply. We have a mature procedure for this and send the guidance with any order that needs holes.

One more honest distinction, because it is asked often: we anneal every acrylic tube as standard, but PC we generally do not anneal. PC's annealing conditions are different and harder to control, so we anneal PC only when the application needs it — and when it does, it is something we have done before, not a first. If you are deciding between the two materials for a part that will be machined or bonded, that difference is worth asking about up front.

Cost, stock and lead time

Cost is the honest reason most parts should stay acrylic. PC runs roughly twenty to thirty per cent more than PMMA, and it is not just the resin — PC has to be dried before extrusion, runs at a higher melt temperature, and costs more energy and more setup scrap. If the part does not need PC, you are paying for a property you will never use.

Stock is the other asymmetry, and it is not the one people expect. We hold acrylic in depth — that is why the acrylic range carries no minimum order. PC we publish as 47 standard round sections, but we deliberately keep PC inventory shallow, because PC ages faster even sitting in a warehouse. We would rather run your PC closer to the order date than ship you material that has been on a shelf longer than it needed to be. That is why PC tends to move on a slightly different clock than acrylic.

When the answer is neither

Finally, the case we have to put in writing because both materials get over-sold here: neither PMMA nor PC likes highly polar oils and greases. A mineral oil is usually fine; a polar oil is not, and the more polar the fluid, the less we will commit to either material until we have tested a sample. If your part sits in a fluid, tell us which one and at what temperature — that single answer decides whether the question is "acrylic or PC" or "neither". Permanent fuel immersion is the same story, and it is covered separately in our fuel and solvent article: that is not an acrylic job, and it is not a PC job either.