Conventional plastic
Polypropylene (PP)
Polypropylene is the tough, heat-tolerant plastic used for food tubs, bottle caps, baby bottles and kettle bodies. It doesn't melt in the microwave, but heating it releases large numbers of tiny plastic particles into food.
By PlasticFreeHome Research Team · Not yet reviewed by an editor · Updated 21 October 2026
- Also called
- PP 5, plastic 5, polypropene
- Recycling code
- 5 (PP)
- Type
- Conventional plastic
- Found in
- food tubs and takeaway containers, bottle caps, baby bottles, kettles, yoghurt pots, tea bag seals, lunchboxes
- Heat
- Survives boiling water and microwaving without melting, but heat sharply increases the particles it sheds. Don't heat food or drink in it.
- Recycling in the UK
- Rigid PP pots, tubs and trays are recyclable in the UK. Most councils collect them; check yours.
What it is
Polypropylene is one of the most common plastics in the world. It's light, cheap, stiff enough to hold its shape and tolerant of heat, which is why it turns up wherever plastic meets hot food: microwave tubs, kettle bodies, baby bottles and the thin layer that heat-seals many paper tea bags.
You'll find it marked with the number 5 inside the recycling triangle, often with the letters PP.
Why heat matters
"Microwave safe" on a PP tub means it won't melt, warp or crack. It doesn't mean nothing moves from the plastic into your food.
Two studies show the size of the effect:
- Microwaving common polypropylene containers released millions of microplastics and billions of nanoplastics from each square centimetre of plastic, far more than storing food in the same tubs at room temperature or in the fridge.
- Polypropylene baby bottles released microplastics during normal formula preparation, and the amount rose with the temperature of the water.
What these particles do inside the body is still being researched. But the exposure is avoidable, and heat is the single biggest driver of it.
Where it touches food
- Microwave and takeaway tubs: the highest-exposure use. Tip food into glass or ceramic before reheating.
- Baby bottles: most plastic bottles are PP. See glass vs steel baby bottles and preparing formula with less plastic.
- Kettles: many have PP bodies or water windows. See kettles with no plastic in the water path.
- Chopping boards: PP boards shed particles as the knife cuts into them.
How to use it more safely
- Keep PP for cold or room-temperature storage.
- Never pour boiling water into it or heat food in it.
- Replace tubs that are scratched, cloudy or warped.
- Swap first where heat is involved: plastic tubs → glass and PP baby bottles → glass.
Recycling
Rigid polypropylene, such as pots, tubs and trays, is recyclable in the UK and most councils collect it at the kerbside. Rinse it first. Soft PP film is a different matter: it goes in supermarket film collections, not your recycling bin.
Related guides
Sources
- Hussain et al. (2023), Environmental Science & Technology — microwaving polypropylene containers and polyethylene pouches released millions of microplastics and billions of nanoplastics per cm²
- Li et al. (2020), Nature Food — polypropylene feeding bottles released microplastics during formula preparation, more at higher temperatures
- Yadav et al. (2023), Environmental Science & Technology — polyethylene and polypropylene chopping boards shed microplastics into food
- WRAP (2022), Polymer choice and recyclability guidance — which plastics are recyclable in the UK, and why PVC and polystyrene are not
Swaps involving PP
Reheating in plastic tubs → glass containers
Heating food in plastic is the single clearest route for plastic particles into what you eat. Glass fixes it.
Swap first · about 600 g of plastic a year
Polypropylene baby bottles → glass or steel
Preparing formula with hot water in plastic bottles releases particles. Glass bottles avoid it.
High priority · about 300 g of plastic a year
Plastic chopping board → hardwood board
Knives cut tiny pieces off plastic boards and into your food. A hardwood board avoids that and lasts for years.
High priority · about 200 g of plastic a year
Plastic tea bags → loose-leaf or plastic-free bags
Many tea bags are sealed with polypropylene or made of plastic mesh. Hot water plus plastic, several times a day; how much reaches your cup is still debated.
High priority · about 120 g of plastic a year
Plastic kettle → steel kettle with no plastic in the water
Boiling water in plastic several times a day is one of the most frequent heat-plus-plastic contacts in a home.
High priority · about 250 g of plastic a year
Plastic lunch box → stainless steel
Steel lunch boxes last for years, go in the dishwasher and don't stain or crack.
Worth doing · about 100 g of plastic a year