PP stands for polypropylene, one of the most widely used plastics in the world. You’ll find the letters “PP” stamped on the bottom of food containers, bottle caps, and storage bins, usually inside or near a triangular recycling symbol with the number 5. It identifies the type of plastic resin the item is made from.
The Number 5 Recycling Symbol
Every common plastic is assigned a resin identification code, a number from 1 to 7 inside a triangle of chasing arrows. PP carries the number 5. This system helps recycling facilities sort materials and helps consumers figure out what they’re dealing with. The other codes you’ll see most often are 1 for PET (water bottles), 2 for HDPE (milk jugs), 3 for PVC, 4 for LDPE (plastic bags), and 6 for polystyrene (foam cups). If you flip over a yogurt tub or a takeout container and see a 5 or the letters PP, you’re holding polypropylene.
What Polypropylene Actually Is
Polypropylene is a thermoplastic polymer derived from petroleum. “Thermoplastic” means it can be melted down and reshaped without breaking down chemically, which is why it’s both moldable during manufacturing and, in theory, recyclable afterward. It resists water, chemicals, and fatigue over time, and it handles heat well compared to many other household plastics. Food containers made from PP won’t warp or melt in the dishwasher, and the material can survive autoclave sterilization, which is why hospitals and labs rely on it.
PP comes in two main varieties. The homopolymer version is stiffer and has a higher melting point. The copolymer version blends in small amounts of ethylene, making it more flexible and better at absorbing impacts, even in cold temperatures, at the cost of slightly lower heat resistance.
Where You’ll Find PP
Polypropylene is everywhere once you start looking. In the kitchen, it shows up as yogurt and cottage cheese tubs (typically sealed with foil lids), reusable food storage containers from brands like Rubbermaid and Sterilite, bottle caps, drinking cups, cutlery, and pitchers. The flip-top lids on ketchup bottles and shampoo caps use PP because it can bend thousands of times at a “living hinge” without cracking.
Beyond food, PP is used in carpets and rugs (it holds color extremely well), ropes, storage boxes, ring binders, wastebaskets, and car batteries. In medicine, it’s the material behind surgical mesh for hernia repairs, nonabsorbable sutures, and a wide range of medical devices. It’s also the key raw material in meltblown fabric, which forms the filter layer in surgical face masks. Industrially, PP shows up in plumbing pipes, roofing membranes, electrical cable insulation, snack food packaging, diapers, and wipes.
Heat Resistance and Microwave Safety
One of the biggest practical reasons people search for PP is to figure out whether a container is safe to microwave. Polypropylene handles heat significantly better than most household plastics. If a container has a #5 recycling code, it is generally considered microwave safe. Many containers also carry a separate microwave-safe symbol: a small microwave icon with wavy lines. Look for both the number 5 and the microwave symbol together for the most confidence.
PP containers won’t melt under normal microwave use, and they’re dishwasher safe on the top rack. That said, repeatedly microwaving any plastic at very high temperatures or for very long periods can degrade it over time, so replacing containers that look warped or discolored is a reasonable habit.
Food Safety
Polypropylene does not contain BPA, a chemical concern associated with some older plastics (particularly polycarbonate, resin code 7). PP also doesn’t typically require phthalates as plasticizers. The FDA has been tightening restrictions on phthalates in food contact materials overall, and testing published between 2018 and 2022 found that manufacturers have been steadily replacing phthalates with alternative compounds. Among common food-grade plastics, PP is widely regarded as one of the safer options for everyday use.
How PP Compares to Other Plastics
PP sits in a middle ground among the plastics you encounter daily. PET (number 1), the clear plastic used for water and soda bottles, is stronger and fully transparent. PP is typically translucent or opaque, so you’ll rarely see it used where crystal clarity matters. HDPE (number 2), found in milk jugs and detergent bottles, is slightly tougher and more impact-resistant, but PP offers better heat tolerance and is lighter. PP has moderate overall strength but excellent chemical resistance, which is why it works so well for containers that hold acidic or fatty foods.
Recycling PP
Polypropylene is picked up through most curbside recycling programs, though acceptance varies by municipality. Despite being technically recyclable, PP recycling rates remain lower than those for PET or HDPE. One challenge is contamination: food residue on yogurt cups and takeout containers can make sorting difficult. Another is that recycling polyolefins like PP requires more careful assessment than recycling PET, because contaminants migrate into the material more readily during repeated processing cycles.
Industry groups like the Polypropylene Recycling Coalition are working to improve these numbers, with a goal of a 5% increase in the U.S. polypropylene recycling rate and plans to deploy $10 million in infrastructure investment through 2025. PP products are not biodegradable, so items that escape the recycling stream persist in the environment for decades. Rinsing your PP containers before tossing them in the recycling bin is the simplest thing you can do to help them actually get recycled rather than sent to landfill.