1. Materials You Should Never Use (Toxic or Degrading under Heat)

Why this matters: At ~212°F some materials chemically break down or release additives. These by-products can migrate into food.

PVC (Polyvinyl Chloride) — avoid

Common in cheap containers, PVC can release hydrogen chloride and plasticizers (phthalates) when heated. Those compounds are associated with endocrine disruption and organ toxicity. PVC is typically labeled as resin code #3 — do not use on heating mats.

Polystyrene / EPS Foam (PS, resin code #6) — avoid

Disposable foam trays and many single-use clamshells are polystyrene. When heated they can leach styrene, a probable human carcinogen. Even brief exposure to elevated temperatures can cause migration into fatty food.

Low-grade epoxy resins and novelty “resin ceramics” — avoid

Some decorative or inexpensive “resin” tableware contain formaldehyde resins or untested additives that can outgas or leach when warm. If an item isn’t certified food-grade and heat-stable, do not use it.

Decorative glazes with metallic finishes — avoid

Gold- or silver-luster glazes or metal leaf in ceramics can oxidize under sustained heat and contaminate food. Unless the manufacturer certifies the glazing as food-safe and heat-stable, avoid.

Bottom line: If a container is disposable, decorative without food-grade labeling, or marked with resin codes #3 or #6, do not place it on a heating mat.

2. Materials Technically Safe but Risky in Practice (Handle with Care)

These won't typically leach toxins at 212°F, but mishandling can cause thermal shock, splintering, or burns.

Regular (soda-lime) glass

Ordinary glass is inexpensive but has a higher coefficient of thermal expansion — uneven contact or sudden temperature change (for example, fridge → hot mat) can cause cracking. For heating mats, prefer borosilicate glass (often labeled "heat resistant" or "borosilicate"), which tolerates thermal change far better.

Practical tip: Avoid placing a cold glass dish directly onto a hot mat; let it come to room temperature first.

Ceramic and glazed porcelain (consumer grade)

High-quality ceramics are usually safe, but cheap or unevenly glazed pieces can develop stress cracks. Metallic glazes are an extra hazard. Choose flat-bottom, oven-safe ceramics without metallic finishes.

Sealed, press-fit lids and airtight containers

Heating builds steam. Vented lids or slightly ajar covers are essential — sealed containers can build pressure and “pop” or shatter. For safety, always provide an escape path for steam.

Handling & burn risk

Materials like glass or ceramic can become hot to the touch. Use oven mitts and allow cooling time. If you must use these containers, adopt precautions: place on an insulated trivet to lift them from the mat when removing.

When using these materials: choose borosilicate glass or verified oven-safe ceramics, vent lids, and avoid sudden temperature changes.

3. Common Safe Materials (Good for Everyday Use, Moderate Heating Performance)

These are broadly safe and non-toxic; the main consideration is thermal conductivity and how evenly they warm.

304 (18/8) stainless steel

304 stainless is the common food-grade steel (nickel-chromium alloy) used for cookware and is non-reactive, corrosion-resistant, and durable. It will not leach harmful substances at heating mat temperatures. Drawback: stainless steel is a moderate conductor — it heats slower than copper and distributes heat less evenly unless the base is engineered (multi-layer base) for conduction.

316 stainless steel

316 stainless includes molybdenum for better corrosion resistance (useful with acidic or salty foods). It shares 304's safety profile and is commonly used in higher-end food containers and professional kitchenware.

Food-grade polypropylene (PP, resin code #5)

PP5 is widely used for reusable lunch containers and is generally heat-tolerant up to ~250°F (120°C). It is a safe, lightweight option for short warmings, though it can warp under sustained heat or direct high-temperature contact.

Food-grade silicone

Silicone is stable (heat-resistant up to ~450°F / 230°C), flexible, and inert. However, silicone is an insulator rather than a conductor — ideal for lids, seals, or protective layers, but not the first choice when you want efficient heat transfer.

Summary: 304/316 stainless steel, PP5, and food-grade silicone are safe. Expect average heat-up speed and possibly minor unevenness unless the cookware bottom is optimized for contact conduction.

4. Recommended Materials — Best Performance + Safety

These materials balance safety, chemical stability, and heat performance — they are the top choices for use with Newkitchen's graphene heating mats.

Borosilicate glass

Borosilicate (commonly sold under terms like "Pyrex" in older marketing) has a low thermal expansion coefficient and can tolerate rapid temperature changes without cracking. It's inert, non-porous, and distributes heat evenly — ideal for soups, casseroles, and mixed dishes.

304 / 316 stainless steel (flat-bottom, well-fitted)

Flat-bottomed 304 or 316 stainless containers make excellent contact with the mat, enabling better conduction. For best results, choose heavier gauge or multi-ply bottom pans that reduce hot or cold spots.

Unglazed stoneware / high-quality ceramic (no metallic finishes)

High-quality stoneware retains heat well and gives long, even warmth for family dining. Ensure the product is labeled oven/microwave safe and free of metallic glazes.

Best practice: For everyday reheating: glass for liquids and casseroles; 304/316 stainless for soups, stews and long meals; stoneware for table serving and retention.

How to Identify Safe Cookware (U.S. Labels & Tests)

A quick checklist helps you identify suitable containers:

• Plastic resin codes: Use #5 (PP). Avoid #3 (PVC) and #6 (PS).
• Heat rating: Look for explicit ratings (e.g., “heat resistant up to 250°F / 120°C” or higher).
• Food-safe / FDA / NSF labels: Manufacturer statements that the product is food-grade and heat tested.
• Oven / microwave safe: These marks indicate the manufacturer has validated thermal performance.
• Material disclosure: Transparent listings such as “Borosilicate glass body; 304 stainless lid” are a good sign.
• Flat bottom: Ensures full contact with the heating mat for even transfer.

Newkitchen’s Graphene Advantage — Faster, Smoother, Safer Heat

Why does the cookware choice become even more important with advanced heating mats? Because Newkitchen’s graphene layer changes the heat dynamics.

What graphene brings to the table

Graphene is a one-atom-thick sheet of carbon arranged in a hexagonal lattice. Its key practical traits for heating:

• Exceptionally high thermal conductivity — graphene conducts heat far more effectively than traditional metals used in mats, enabling the pad to reach target temperature rapidly.
• Uniform thermal spread — instead of a few hot wires, heat is distributed across the full surface, removing hot/cold spots.
• Energy efficiency — faster equilibration means less energy wasted in ramping up and more steady warmth during use.
• Stable operation — graphene films are thin, flexible, and durable when embedded properly and protected by food-grade silicone layers.

Real benefits when paired with recommended cookware

When Newkitchen’s graphene mat is used with borosilicate glass or flat-bottom 316 stainless steel:

• 30% faster effective warm-up compared to traditional wire mats — your meal is ready to eat sooner.
• Even temperature across the entire base — no cold centers, no scorched edges.
• Better texture retention — rice retains fluff, sauces remain glossy, and proteins do not toughen from rapid local overheating.
• Lower power draw due to rapid thermal equilibrium.

Think of graphene as replacing a handful of discrete space heaters with a single gentle, evenly warm sheet — like sunlight warming a field rather than a spotlight burning a spot.

Practical Use & Safety Tips

• Always use flat-bottom cookware to maximize contact area.
• Avoid metal trays that may retain heat dangerously; if using stainless, ensure the mat manufacturer permits metal contact (follow product manual).
• Vent sealed lids to prevent pressure buildup — pierce film or leave a small vent.
• Do not place a frozen dish directly onto a hot mat; allow it to thaw slightly to avoid thermal shock.
• Use oven mitts when removing containers and place on trivet; surfaces and glass get hot even if the mat is low-voltage.
• Inspect containers periodically for warping, crazing (fine cracks in glaze), or odor changes; discard questionable items.

Quick Reference Table

Conclusion

Choosing the right container for reheating is a small habit that pays back in health, flavor, and energy savings. Pairing safe, high-performance materials (borosilicate glass, 304/316 stainless, unglazed stoneware) with Newkitchen’s graphene heating mats yields the fastest, most even, and most food-respecting reheating experience available in the consumer market today.

For more about the science behind our graphene mats and how to get the most from them, visit: Graphene Explained: What Makes It the Future of Heating Technology.

Explore Newkitchen Graphene Heating Mats