Table of Contents
Reviewed and updated by ICD - Week 43/2026
The surest way to tell what a bottle is made of is the resin code on its base: number 1 is PET, number 2 is HDPE, number 4 is LDPE, number 5 is PP. When there is no code, three clues help tell PE bottles from PET and PP: clarity, a waxy feel to the touch, and a float test in water. This guide walks through each method, with the heat tolerance of each type so that hot liquids are not poured into the wrong bottle.
1. Why it matters
Each plastic has a different heat tolerance and recycling route. A PET bottle holding hot water will soften and warp, and a PE bottle that ends up in a PET recycling batch ruins the whole batch because the two plastics do not mix. Sorting correctly also tells you which bottles can be reused and which are single-use.
2. Method 1: read the resin code
The resin code is a triangle of arrows with a number inside, usually embossed on the base of the bottle in the numbering system from 1 to 7 (Wikipedia, Resin identification code). The code identifies only the plastic type; it is not a mark that the bottle is safe for food.
| Code | Plastic | Common bottles | Melting or softening point |
|---|---|---|---|
| 1 | PET | Water, soft drink and cooking oil bottles | Tm about 253 °C, Tg about 75 °C |
| 2 | HDPE | Milk, shampoo, detergent bottles, jerrycans | Tm about 128 °C |
| 3 | PVC | Industrial bottles, pipes, building materials | Amorphous, Tg about 80 °C |
| 4 | LDPE | Squeeze bottles, bags, film | Tm about 110 °C |
| 5 | PP | Jars, food boxes, heat-sterilized bottles | Tm about 163 °C |
The thermal points are taken from the DSC Tg and Tm table of Kunststoff-Profi. Two notes: PET has a high melting point but its glass transition is only about 75 °C, so the bottle softens when boiling water is poured in; PVC has no clear melting point because it is an amorphous plastic.
3. Method 2: identify by eye and hand
HDPE bottles are usually opaque white or colored, with fairly thick walls and a slightly slippery, waxy surface, and a hard squeeze followed by release often leaves a crease. LDPE bottles are softer and spring back to their shape when squeezed. PET bottles are glass-clear, stiff and brittle when folded. PP bottles are opaque or colored, stiff but very elastic, and hard to crease white.
4. Method 3: float test and burn test
PE and PP both have a density under 1 g/cm³ so both float on water, while PET and PVC are denser than water and sink. The float test therefore separates PE and PP from PET and PVC, but cannot separate PE from PP.
The burn test is only a rough identification; do it outdoors with good ventilation using a small sample. According to the Boedeker table, PE burns with a blue flame with a yellow tip, smells like paraffin wax and drips. Additives such as flame retardants can mask the burning behavior of the base plastic, so the result must be checked against the resin code and not used alone.
5. PE, PET and PP: which bottle for which job
| Criterion | Chai PE (HDPE, LDPE) | Chai PET | Chai PP |
|---|---|---|---|
| Clarity | Opaque or milky white | Very clear | Opaque or colored |
| Heat tolerance | Softens early: HDT about 38 - 69 °C under load | Glass transition about 75 °C | Better heat tolerance than PE: Tm about 163 °C |
| Hot water, microwave reheating | No | No | Yes if labeled microwave-safe |
| Suited to | Milk, shampoo, detergents, goods that need hard shaking or impact | Carbonated drinks, bottled water | Reheated food, heat-sterilized bottles |
| US bottle recycling rate 2018 | 29.3% for natural-color HDPE bottles | 29.1% for PET bottles | no separate figure |
The HDT figures come from the Piedmont Plastics LDPE datasheet (38 °C) and the GEHR HDPE datasheet (69 °C). The recycling rates are US Environmental Protection Agency figures for bottles and do not reflect Vietnam.
For food containers, virgin food-grade plastic is a requirement common to all three types under rules such as 21 CFR 177.1520. A resin code cannot replace this certification.
Frequently asked questions
How do I know whether a plastic bottle is PE?
Look at the resin code on the base: number 2 is HDPE, number 4 is LDPE. PE bottles are usually opaque, softer than PET, float on water, and in a burn test give a blue flame with a yellow tip and a wax smell.
Which plastic bottles can hold hot water?
PP labeled microwave-safe is the familiar choice; PE and PET both soften at lower temperatures, so boiling water should not be poured into a PE or PET bottle.
Can PET plastic bottles hold hot water?
They should not. PET has a glass transition at about 75 °C, so the bottle softens and warps with boiling water.
Which type are milky-white plastic bottles usually?
Usually HDPE (code 2), such as milk and shampoo bottles. To be sure, check the resin code on the base.
Can PE plastic bottles be recycled?
Yes. Natural-color HDPE bottles are among the most recycled plastics: 29.3% in the US in 2018 according to the EPA.
How do LDPE bottles differ from HDPE?
LDPE is soft and flexible, usually squeeze bottles, bags and film; HDPE is stiffer and tougher, used for milk bottles, jerrycans and crates.
Contact ICD Vietnam for advice
ICD Vietnam Industrial Manufacturing Co., Ltd.
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References
- Wikipedia, Resin identification code (resin codes 1 to 7 under ASTM D7611) - en.wikipedia.org
- Kunststoff-Profi, Glass Transition & Melting Temperature of Plastics (DSC table of Tg and Tm) - kunststoff-profi.de
- Boedeker Plastics, Plastic Identification (burn test) - boedeker.com
- Piedmont Plastics, LDPE (continuous use up to 80 °C, Vicat 85 °C, HDT 38 °C at 0.46 MPa) - piedmontplastics.com
- GEHR, Technical Data Sheet PE-HD (melting 130 °C, Vicat 125 °C, HDT 69 °C, continuous use up to 90 °C per UL 746B) - en.gehr.de
- US EPA, Plastics: Material-Specific Data (natural HDPE bottles 29.3%, PET bottles 29.1% in 2018) - epa.gov
- 21 CFR 177.1520, Olefin polymers (Cornell LII) - law.cornell.edu
