PET vs PP vs HIPS Thermoformed Tray: Material Properties & Application Comparison

Overview #

Choosing the wrong substrate for a thermoformed tray is one of the most common and costly mistakes we see in new product briefs — it affects not just structural performance but downstream filling line compatibility, retail presentation, and regulatory compliance. This article covers the three substrates we work with most on our thermoforming lines: PET (polyethylene terephthalate), PP (polypropylene), and HIPS (high-impact polystyrene). The guidance applies directly to brands in food, cosmetics, electronics, and pharmaceutical secondary packaging who are specifying trays for the first time or switching suppliers. The single most important production insight: material selection must be locked before tooling is cut, because a mold designed for 0.5mm HIPS cannot simply be rerun in 0.7mm PET without dimensional drift and draw ratio recalculation.

Material Properties: What Each Substrate Actually Does on the Forming Line #

When a brief lands on our structural design desk, the first question is always: what is the tray doing — protecting, presenting, or both? The answer drives substrate selection before we even open the CAD file.

PET (APET/RPET) is our default recommendation for retail-visible trays where clarity is non-negotiable. Optical clarity on APET sheet runs 88–92% light transmission, and it thermoforms cleanly at sheet temperatures of 130–160°C. Tensile strength is typically 55–75 MPa (ASTM D638), which gives good puncture resistance for cosmetic inserts and food trays. RPET (recycled content) is available in 30%, 50%, and 100% post-consumer recycled grades — we run RPET on dedicated lines to avoid cross-contamination and can certify recycled content to ISO 14021. One limitation: PET has poor chemical resistance to strong alkalis and is not suitable for trays that will contact aggressive cleaning agents.

PP (polypropylene) is the substrate we specify when the tray needs to survive heat — either hot-fill food applications (up to 121°C retort in some grades) or sterilisation cycles in medical secondary packaging. PP sheet thermoforms at 160–180°C and has a flexural modulus of 1,100–1,600 MPa (ASTM D790), making it stiffer than HIPS at equivalent gauge. The trade-off is optical clarity: natural PP is translucent, not clear. For applications where the product needs to be visible, we use clarified PP grades, which reach 70–80% light transmission — acceptable for many food trays but not for premium cosmetic presentation. PP is also the only substrate among these three that is fully compatible with microwave applications.

HIPS (high-impact polystyrene) is the workhorse of our electronics and industrial insert lines. It thermoforms at 150–175°C, accepts printing and painting well, and is the easiest of the three to form into deep-draw geometries with draft angles as tight as 2°. Tensile strength is lower — typically 25–40 MPa — but for protective inserts where the tray is inside a corrugated shipper, this is rarely the limiting factor. HIPS is opaque by default and available in a full colour range, which makes it the preferred choice for branded electronics inserts where the tray itself carries colour identity. The key restriction: HIPS is not food-contact approved under EU Regulation 10/2011 or FDA 21 CFR 177.1640 for direct food contact, so it is limited to non-food applications in our production planning.

Structural Parameters: Gauge, Draw Ratio, and Dimensional Tolerances #

Getting the gauge specification right is where most briefs need the most guidance. Brands often specify a finished tray wall thickness without accounting for material thinning during the draw — on a deep-draw tray with a draw ratio of 1:1.5, the sidewall can thin by 30–45% from the nominal sheet gauge. We always calculate minimum wall thickness at the deepest point of the cavity before confirming a gauge recommendation.

Our standard dimensional tolerance on thermoformed trays is ±0.3mm on cavity length and width, and ±0.5mm on depth — tighter than this requires matched-metal tooling rather than our standard plug-assist vacuum forming setup, which adds 15–20% to tooling cost.

For food-contact applications, we require material certification to EU Regulation 10/2011 (plastics in contact with food) or FDA 21 CFR Part 177 as applicable to the destination market. We maintain supplier declarations of conformity for all food-grade PET and PP sheet stock on file and can provide these as part of our quality documentation package.

Quality Control and Compliance Parameters #

On our thermoforming lines, we run AQL 2.5 sampling inspection on dimensional checks and AQL 1.5 on visual defects (voids, webbing, whitening at corners) for food and pharmaceutical tray orders. For electronics insert trays, we apply ESD-dissipative HIPS where the customer specifies surface resistivity between 10⁶ and 10⁹ ohms (IEC 61340-5-1).

For RPET trays destined for EU markets, we track recycled content percentage per batch and can provide documentation aligned with the EU Packaging and Packaging Waste Regulation (PPWR) requirements for recycled content claims. Our RPET sheet suppliers hold GRS (Global Recycled Standard) certification, and we can pass through chain-of-custody documentation on request.

Seal integrity for lidded food trays is tested per ASTM F2096 (bubble emission) and ASTM F1929 (dye penetration) — we recommend brands specify a minimum seal strength of 1.5 N/15mm for peel-open retail trays and 3.0 N/15mm for tamper-evident applications.

Specification Notes for Brand Partners #

When you brief us on a thermoformed tray project, the most useful information you can give us upfront is: the product dimensions and weight, the intended filling method (manual, semi-auto, or automated line), the destination market (which drives food-contact compliance requirements), and whether the tray will be visible to the consumer at retail or hidden inside a shipper.

The most common brief mistake we see is specifying gauge based on a competitor’s tray without accounting for the draw ratio of your specific cavity geometry. A 0.5mm PET sheet that works perfectly for a shallow cosmetic tray with a 15mm draw depth will produce unacceptable corner thinning on a 40mm deep electronics insert — we will always recalculate and flag this before tooling is cut.

Our typical process: structural design review and DFM feedback in 3–5 working days, tooling fabrication in 15–20 working days, first physical samples in 20–25 working days from brief approval. Production lead time after sample sign-off is 15–20 working days for standard orders. MOQ on thermoformed trays starts at 5,000 units for existing tooling and 10,000 units for new tooling amortisation.

Frequently Asked Questions #

Q1: What is the minimum wall thickness we should specify for a PET food tray with a 35mm draw depth?
A: Starting from a 0.5mm APET sheet, a 35mm draw depth at a 1:1.2 draw ratio will produce sidewall thinning of approximately 30–40%, leaving a minimum wall of around 0.30–0.35mm at the cavity corners. For most retail food trays, we recommend a minimum finished wall of 0.30mm — if your product weight exceeds 300g, we would move to 0.6mm sheet to maintain structural integrity.

Q2: What is your MOQ and lead time for a new thermoformed tray with custom tooling?
A: Our MOQ for new tooling projects is 10,000 units to amortise tooling cost. Tooling fabrication takes 15–20 working days, and first physical samples are typically ready 20–25 working days from brief approval. Production lead time after sample sign-off runs 15–20 working days depending on order volume and substrate availability.

Q3: Can HIPS trays be used for food packaging in the EU or US markets?
A: No — HIPS (polystyrene) is not approved for direct food contact under EU Regulation 10/2011 or FDA 21 CFR 177.1640 for most food applications. For food trays, we specify APET or food-grade PP, both of which we can supply with full supplier declarations of conformity for EU and US market entry.

Q4: Can you produce RPET trays with certified recycled content for EU sustainability compliance?
A: Yes — we run RPET in 30%, 50%, and 100% post-consumer recycled grades on dedicated lines. Our sheet suppliers hold GRS certification, and we provide chain-of-custody documentation aligned with EU PPWR recycled content requirements. Optical clarity on RPET is marginally lower than virgin APET but typically within 85–90% light transmission on well-processed sheet.

Q5: What causes corner whitening on PP trays and how do you prevent it?
A: Corner whitening on PP is caused by stress-whitening when the material is drawn beyond its optimal elongation at forming temperature — typically when the sheet temperature drops below 155°C before the plug contacts the material, or when the draw ratio exceeds 1:1.5 on standard PP grades. We control this by monitoring sheet surface temperature with infrared sensors at ±3°C tolerance and using clarified PP grades with higher elongation at break (>400% per ASTM D638) for deep-draw geometries.

Planning a thermoformed tray project? Contact our team to request a complimentary specification review and sample quote.