The triangle with a number is the Resin Identification Code (RIC) that indicates the plastic type used. You’ll see it on many triangular cake and sandwich containers.

• Material ID: The number identifies the resin (e.g., 1 = PET, 5 = PP).
• Usage cues: As a general guide, disposable clear dessert boxes are often PET, while reusable lunch keepers are frequently PP.
• Not a safety rating: RIC isn’t a guarantee of food safety or heat resistance; rely on food-grade, microwave, or freezer icons.
• Recycling varies: Local programs differ, so check local guidance.

For best results, review each item’s description and care instructions on Walmart.com before using or heating.

“Triangle 5” refers to polypropylene (#5), a material commonly used in reusable food containers because it’s durable and handles moderate heat. Many triangle sandwich keepers use PP.

• Look for labels: Check the product page for “food-grade” and “microwave-safe” icons before reheating.
• Typical uses: Suitable for sandwiches, meal prep, and leftovers in reusable containers.
• Heat practices: Use medium microwave power and vent the lid to reduce steam buildup.
• Inspect wear: Replace containers that are cracked or warped.

Disposable triangle dessert boxes are often PET (#1) and intended for cold or room-temperature foods. Always follow the care notes provided in each item’s description.

Some can be microwaved, but not all. Many reusable, food‑grade plastic or silicone triangle containers are labeled microwave‑safe, while clear hinged dessert boxes are typically not intended for heating.

• Check icons: Look for a microwave symbol or heating instructions on the product page.
• Vent lids: Loosen or open the lid slightly so steam can escape.
• Use medium power: Short intervals help reduce warping and hot spots.
• Avoid long cooks: For oily or sugary foods, consider transferring to a microwave‑safe plate if you’re unsure.

Following the manufacturer’s care instructions can help preserve the container’s seal and shape over time.

Both work—choose based on how you plan to pack and serve.

• Reusable: Often leak‑resistant, washable, and sometimes microwave‑safe—good for everyday lunches, snacks, and leftovers.
• Disposable: Clear, stackable options with hinged lids or tamper‑evident seals are convenient for bake sales, catering, or sharing treats.
• Heating: If you’ll reheat, reusable versions marked microwave‑safe are typically a better fit.
• Quantity: Multi‑packs of disposables can simplify packing for larger groups.

Compare capacity, dimensions, and care icons on Walmart.com to match your routine. Availability and features vary by item and intended use.

Start by measuring your slice and matching those dimensions to the box.

• Measure length: Tip to crust. Many listings note lengths around 4.3–5 inches.
• Measure width and height: Back‑of‑slice width and frosting height so the hinged lid clears toppings.
• Match to cake size: Some boxes indicate they fit slices from 6–8 inch cakes—use this as a general guide.
• Transport needs: Choose stackable containers or tamper‑evident designs if you’re traveling or selling.

When unsure, a slightly larger container can help prevent pressing frosting or decorations, while still keeping the slice secure.