The "Polycarbonate" Display Stands Turned Yellow and Cracked Within a Month

Polycarbonate vs Acrylic vs PET Clear Plastic Verification Guide

Hello, this is StartMade.

A household goods brand with products in about 40 retail stores across Korea had an acrylic products factory in Dongguan (东莞), Guangdong, make 1,200 clear display stands. Each stand had a stepped body bent from 4mm clear polycarbonate (PC) sheet, with two shelves of the same PC fixed by screws. Store staff take products in and out of these stands many times a day, so the brand chose "PC that won't break when dropped" on purpose and paid nearly 30% more per unit than for acrylic. The sample bent without breaking, and at pre-shipment inspection, dimensions, clarity, scratches and assembly all passed.

About three weeks after the stands went into stores, the calls started. Shelves on stands near windows had turned visibly yellow, and in several stores fine cracks spread like a spider web from the screw holes. A shelf dropped while restocking shattered into sharp pieces. Remaining stock went to a lab for infrared spectroscopy (FTIR). The body was PC, but recycled resin had been mixed in, so it was slightly yellow from the start, and the two shelves were not PC at all but 3mm acrylic (PMMA). The alcohol cleaner used in the stores had attacked the acrylic around the screw holes, where tightening had left stress, and cracked it. The factory's explanation was short: "亚克力和PC看起来一样，激光切割更方便" (acrylic and PC look the same, and laser cutting is easier).

Clear plastics all look alike. They are equally transparent and glossy, and when new you can hardly tell them apart by touch. The differences only show up weeks later, after sunlight, cleaners and impacts have done their work. This post covers the differences between clear materials such as PC, acrylic, PET, PETG and PS, the checks you can use on site and the limits of each, approximate criteria, gaps in material certificates, common supplier substitutions, and what to check in the spec sheet and at inspection.

"It's PC material" and a single resin datasheet are not enough. Write the material, resin grade, thickness and whether recycled resin is allowed for every part into the spec sheet, confirm the material on samples you pick yourself from production, and test impact, heat resistance and discoloration to prevent the yellowing, cracking and breakage that appear weeks later.

1. Why Products That Passed Inspection Fail Within Weeks

Pre-shipment inspection is mostly about looking and measuring. Inspectors check dimensions, scratches, bubbles, clarity and assembly, and on those items PC, acrylic and PET give almost identical results. Material differences only appear after time and the environment have had their effect.

Yellowing is usually the first sign. PC without a UV stabilizer, or with recycled resin mixed in, yellows quickly under sunlight and fluorescent lights, and recycled resin that is slightly yellow from the start only shows when several clear products sit side by side. Cracks come next. When alcohol, cleaners or hand cream touch stressed areas of acrylic or PC, such as screw holes, bent corners and press-fit joints, environmental stress cracking spreads fine crazing, and laser-cut acrylic edges are especially weak because of residual stress.

The difference when dropped is even more dramatic. PC has dozens of times the impact strength of acrylic, so if a product you bought as PC is actually acrylic or PS, one drop to the floor is the end of it. For water bottles and cups, heat is also a problem. PET and PETG start to soften at around 70°C, so a bottle switched to PET loses its shape after one cup of hot tea or one dishwasher cycle.

We covered how yellowing works and lightfastness testing in Episode 131 and plastic resin grades in general in Episode 125. This post deals only with one clear material being swapped for another.

2. Five Clear Plastics and How They Differ

Factory quotes mix many names, such as "PC," "亚克力," "PET," "有机玻璃" and "透明料." On Chinese shop floors, acrylic is also called "有机玻璃" (organic glass) or "压克力," PC sheet is called "耐力板," and clear PS is called "透明PS" or "GPPS." You need to know the actual properties, not just the names, to spot a substitution.

BPA-free copolyesters such as Tritan also show up often in water bottles. Tritan is a resin company's trademark, so the word "Tritan" alone tells you nothing about the actual resin; you need the resin grade and proof of purchase as well. For food contact products, material choice ties directly into import requirements, so see Episode 64 too.

3. Checks Compared — From Hand Tests to Spectrometers

Ask a factory "这是PC吗?" (is this PC?) and the answer is almost always "是PC" (yes, PC). The only way to verify that answer is to test it yourself, and each method has clear strengths and limits.

How to Read a Burn Test

Only burn offcuts, and only with the factory's consent. PC is hard to ignite and tends to go out soon after the flame is removed, charring with black soot as the surface bubbles up. Acrylic catches easily and keeps burning after the flame is removed, with almost no soot, a sweetish smell similar to nail polish, and a crackling sound. PET and PETG drip as they burn with a yellow flame, and PS sends up streams of thick black soot. Flame-retardant grades and blended resins blur these differences, so use the burn test only to decide whether something is suspicious.

Specific Gravity Is Strong for Separating PS and PET

Specific gravity is calculated by weighing a sample once in air and once in water. A scale reading to 0.01g and a cup of water are enough. PS is 1.04–1.05, PETG 1.27 and PET 1.33 or more, so they separate clearly from PC and acrylic. PC (about 1.20) and acrylic (about 1.18–1.19), on the other hand, fall within measurement error of each other, so specific gravity alone can't decide between them. To separate PC from acrylic, combine it with bending, burn or solvent tests or a spectrometer.

A Spectrometer Only Tells You the Material Name

Handheld near-infrared (NIR) or Raman spectrometers are now used to identify materials on the spot at inspection. Clear materials read well, so they fit nicely into pre-shipment inspection. But even when a spectrometer says "PC," it won't tell you how much recycled resin is in it, whether a UV stabilizer was added or whether the thickness matches the spec. That is why material identification should always come bundled with thickness measurement, yellowness comparison and impact testing.

4. Approximate Criteria

These are condensed from resin manufacturers' datasheets and values commonly referenced in the industry. The same material varies a lot by grade, so set your actual criteria from the datasheet of the resin grade you specify.

The biggest gap in the table is impact strength. PC is dozens of times tougher than acrylic or PS, with PETG in between. Light transmission is actually highest for acrylic, so "even clearer than PC" can be a sign that the factory switched to acrylic. For finished goods, criteria like the following are easier to use directly at inspection than raw material properties.

• Yellowness index (YI): Set it against the approved sample, and if production units read several points higher, suspect recycled resin or a resin change.
• Thickness: ±5–10% of nominal thickness is a common sheet tolerance. If a 4mm order measures under 3.6mm, check whether the thickness was reduced.
• Drop and falling ball impact: Write conditions and pass criteria in numbers, for example "no breakage in a 1m free fall onto concrete" or "no penetration or cracking from a 500g steel ball dropped from 1m."
• Heat and washing: For bottles and cups, use real-use conditions such as "no deformation after 30 minutes in 90°C water" or "no whitening or cracking after 20 dishwasher cycles."

5. Gaps in Material Certificates and "PC Material" Claims

Ask for proof of material and the factory usually sends a resin datasheet, a UL yellow card or a lab report. The documents are rarely fake. They simply aren't connected to the product being made now.

6. Common Supplier Substitutions

Clear materials look almost the same, yet the price gap is significant. Based on 2026 domestic sheet prices in China, PC often costs roughly 20–40% more than acrylic and nearly twice as much as PET. Acrylic is also much easier to work, cutting straight on a laser with clear edges. When cost pressure comes, the factory touches the material first. Here are the types we have actually encountered in consultations.

The most common is changing only the small parts. With a PC body, the factory can say "主体是PC" (the body is PC) with a straight face, and inspectors tend to check only the large parts and move on. We covered molds and resin control in Episode 33 and the process for requiring prior approval of material and part changes in Episode 119.

7. The Cost When the Material Changes

Clear material problems surface after the product is sold, and once they do, they spread to the whole lot.

• Full replacement: Even if only some display stands or cases break, the whole lot can no longer be trusted, and you end up replacing all of it.
• Safety incidents: Acrylic and PS break into sharp pieces. For store fixtures or children's products, that can lead to injuries.
• Reviews and returns: When bottles yellow or case corners crack, one-star reviews pile up with photos, and the seller pays for returns.
• Regulatory issues: PC bottles and food containers face bisphenol A restrictions in many markets. If the spec sheet doesn't state the material precisely, even working out which rules apply gets tangled.

See Episode 53 for recalls and product liability and Episode 36 for claims and dispute handling.

8. Items to Put in the Spec Sheet

Factories each read a single line of "透明PC" differently. Put the items below into a table and attach it to the spec sheet.

The most effective item is specifying material per part. Once even the small parts have a material written next to them, the moment the factory switches one shelf to acrylic it is in breach of contract. See Episode 59 for how to write spec sheets and BOMs.

9. Adding Material Checks to Your QC Checklist

Sample Stage

At the sample stage you set the baseline. Confirm the material of each part with a spectrometer or lab FTIR, and record thickness, weight and specific gravity. Running falling ball impact, hot water and cleaner tests on the same sample gives you a reference to compare production against. Seal the approved sample with the date and part number and keep it out of the light, or you won't be able to compare yellowness later. We covered sample management in Episode 34.

Production Stage

On the day resin or sheet arrives at the factory, get photos of the bag labels, sheet protective film and delivery notes. It also helps to check what sheet is stacked next to the laser cutter and whether there are bags of recycled resin next to the grinder. See Episode 102 for production tracking.

Pre-Shipment Inspection Stage

The inspector picks packed products personally, checks the material of each part, and compares thickness and weight with the sample records. Placing units next to the approved sample on white paper makes any yellow tint easy to see. Drop and hot water tests on just a few units can catch a lot where the material was changed. If anything looks suspicious, seal random samples and send them to a lab. Pre-shipment inspection is covered in Episode 100.

10. Example Request Wording for the Factory

Putting the wording below into your purchase order or spec sheet takes material choice out of the factory's hands and makes it easier to assign responsibility if something goes wrong.

"本产品所有透明部件（主体、层板、盖板等）须使用聚碳酸酯（PC），原料或板材须使用规格书指定的厂家及牌号，不得使用亚克力（PMMA）、PET、PETG、PS或其他材料替代。板材厚度4.0mm±0.2mm，禁止使用回收料、破碎料及未做抗UV处理的板材。如需更改材质、原料、板材供应商或厚度，须提前书面确认。生产时请提供原料包装标签或板材保护膜的照片。出货前由我方从成品中随机抽样，按部件进行材质鉴定、厚度测量、与确认样的黄变对比及1米跌落测试，如不合格，整批返工或退货，检测及物流费用由供应商承担。"

11. Three Real Cases

These are anonymized versions of patterns we often encounter in consultations. Amounts and figures are examples.

Case 1 — Clear Display Stands for Retail Stores

This is the case from the opening. The purchase order said only "透明PC 4mm" and didn't mention the shelves separately, so the factory tried to deny responsibility, saying "we made the body in PC." Only after the brand put the lab results and sample photos on the table was it settled, with the factory covering most of the cost of remaking 2,400 shelves in PC, while the brand paid to replace some of the yellowed bodies. Purchase orders now come with a part-by-part material table.

Case 2 — Outdoor Water Bottles

A company that sourced "BPA-free PC alternative" water bottles from a household goods factory in Taizhou (台州), Zhejiang, started getting reviews a month after launch saying "the bottle shriveled when I poured in hot water." Measuring specific gravity gave 1.27: PETG. The factory insisted it was "BPA-free" just like the sample, but the spec sheet had neither a material name nor a heat condition. From the next order, the company added the resin grade and a condition of "no deformation after 30 minutes in 90°C water," and now runs a hot water test before shipment.

Case 3 — Clear Hard Tablet Cases

A seller importing clear PC hard cases from Shenzhen saw returns rise from the second lot on, with complaints like "it turned yellow within weeks" and "the corner broke when I dropped it." The material read as PC, but next to the first lot the new lot had a yellow tint from the start and visible black specks. At the lab, its melt flow index (MFI) came out much higher than the first lot's, pointing to degraded recycled resin mixed in. The spectrometer had called it PC, so relying on material identification alone, the seller would never have found the cause.

12. Common Mistakes

The most common is ending the check once the factory sends a resin datasheet. A datasheet can't tell you whether that resin actually went into your product. We also often see buyers check only the body and skip parts like shelves and lids, conclude it must be PC because the specific gravity is around 1.2 (acrylic gives the same value), or assume there is no recycled resin because a spectrometer said PC. For bottles and cups, inspecting only at room temperature and skipping the hot water test causes the biggest trouble later.

13. Clear Plastic Material Control Checklist

Sample Stage

• Wrote the material (polymer name), resin grade, thickness and recycled resin policy for each part into the spec sheet
• Confirmed the material of each part of the approved sample with a spectrometer or FTIR
• Recorded baseline thickness, weight, specific gravity and yellowness
• Kept results of drop and falling ball impact, hot water and cleaner tests
• Sealed the approved sample and stored it out of the light

Production Stage

• Received photos of resin bag labels or sheet protective film
• Checked the sheet and resin on the shop floor and whether recycled resin bags were present
• Applied material, resin or thickness change requests only after written approval

Pre-Shipment Inspection Stage

• Checked the material of each part of randomly picked finished goods
• Measured thickness and weight and compared with sample records
• Compared yellow tint and black specks side by side with the approved sample
• Ran a drop test and, where relevant, a hot water test

Wrap-Up - Check What It's Made Of, Not Just That It's Clear

Whether it is PC, acrylic or PETG, a clear product leaving the factory sparkles and looks just as transparent. The difference shows weeks later by a store window, in a customer's dishwasher or the moment it hits the floor, and by then the whole shipment has already been sold. Writing materials and resins per part into the spec sheet and checking the material, thickness, color and impact performance of samples pulled from production costs far less than the full replacements and returns you would pay for later.

There is also something you can do right now. Ask the factory currently in production for a table of materials and resin grades by part, along with photos of the resin bags or sheet protective film. If the only answer is "都是PC，放心" (it's all PC, don't worry), build a material control sheet and send it before your next order.

StartMade supports you with spec sheets that set materials and resin grades per part, review of supplier material documents, checks of incoming resin and sheet during production, and pre-shipment inspection including material identification and thickness, discoloration and impact checks. If you have already faced yellowing or breakage, we start by analyzing the remaining stock; if you are preparing a new product, we start with the spec sheet together.