A failed transparent product is unforgiving. A scratch, a bubble, a clip that snaps on first use: the customer sees everything, and lets you know. Material choice is not a technical detail, it is a product decision. Polycarbonate (PC) or polymethyl methacrylate (PMMA, also known as Plexiglas): these two transparent plastics cover most cases, but they do not fit the same contexts.
The MusiWall case: a clip-on vinyl display for music lovers
In 2021, Julien Paeschen launched MusiWall, a solution to hang vinyl record sleeves on the wall with elegance, without damaging the wall and without a bulky frame. The product runs on a simple principle: a transparent framing clip that holds a 33 rpm sleeve and lets you swap it in seconds.
The brief gave us two hard constraints: maximum optical transparency (the clip must visually disappear to let the sleeve shine) and dimensional precision (the clip must snap at the right force, firmly hold a 33 rpm sleeve without marking it, and survive thousands of mount/unmount cycles).
Our choice: injected polycarbonate, mirror-polished steel mould, 10,000-unit production run. The finished product is on musiwall.com.
Why polycarbonate and not PMMA
PMMA has slightly better transparency than PC (around 92% light transmission versus 88%). On paper, PMMA wins. In the real life of a product that snaps thousands of times, it loses.
Impact resistance: PMMA is brittle. A PMMA part dropped from a metre shatters. PC absorbs impact without cracking. For a product handled every day, PC wins.
Repeated flexing: the MusiWall clip has to open and spring back. Tens of thousands of times. PC holds up under cyclic stress, PMMA fatigues and eventually snaps.
Heat resistance: a vinyl sleeve near a window can heat up. PC holds up to around 135 °C in continuous use, PMMA gives out at 85 °C.
The solution: PC for anything functional and transparent. PMMA for anything decorative and transparent (display cases, static objects, light diffusers).
Making a mould for a transparent part: everything changes
Many subcontractors accept a transparent project without telling the customer that a mould for transparent material is not a standard mould. Everything shifts: cavity finish in A1 mirror polish (optical grade), not textured (any micro-defect shows), higher mould temperature (typically 85 to 120 °C for PC) to avoid visible flow lines, rigorous purging before series start, and strict material filtration to eliminate residual pigment or micro-contamination.
⚠️ Warning: some manufacturers use entry-level moulds with rough polish and compensate with surface treatment (varnish, piece-by-piece polishing). It costs more over time and quality drifts. Always demand a mirror polish from the start.
Dimensional precision: what locked in the MusiWall product
On a clip part, the tolerance on the active zone makes or breaks the product. Too tight, the sleeve gets marked. Too loose, it falls. For MusiWall, we worked to within a tenth of a millimetre on the clamping zone, with a hardened steel mould guaranteeing dimensional stability across the whole run.
Our tip: during trials, we inject 50 parts, then Julien tests them on 10 different sleeves (cardboard thickness variations). Corrections are made on the mould before the production run, not after. Launching a 10,000-unit run on an unvalidated mould means 10,000 parts to rework or scrap.
What we deliver
Mould design and validation in mirror polish, mould build in 6 to 8 weeks, trials and fine-tuning, series production with dimensional control on a reference part, and final packaging. For MusiWall: from the first sketch of the idea to delivery of 10,000 packaged units.
Got a transparent product project?
Send us your 3D file or even a simple sketch. We review feasibility free of charge: material choice (PC, PMMA, or an alternative you may not have considered such as MABS), mould choice, cavity count, cycle calibration. Full quote within 5 working days.
FAQ
What is the price difference between PC and PMMA?
It varies with the supplier and the grade, but both materials sit in a similar range. The choice should be made on performance, not on the raw material.
Does PC yellow in sunlight?
Standard grades do, over several years of direct exposure. For parts used outdoors, use a UV-stabilised PC grade. Indoors (the MusiWall case), no issue.
Can transparent PC be tinted?
Yes. Crystal PC, smoked, bluish, or custom pigmented. Transparency is kept as long as the pigment is translucent.
From what volume does a transparent mould become relevant?
From roughly 1,000 parts, depending on complexity. Below that, transparent 3D printing or bulk machining stay more suitable.
How long did the MusiWall project take?
Mould in 6 to 8 weeks, trials and corrections in 2 weeks, first series in 3 weeks. Around 3 months in total from go-ahead to delivered stock.
