Plastic ice cubes are filled with distilled or purified water sealed inside a food-safe, BPA-free plastic shell. Some versions contain a small amount of preservative or thickener mixed into the water, but the core ingredient is simply water that freezes and thaws inside a sealed container. The idea is straightforward: the water inside does the cooling, while the plastic keeps it from diluting your drink.
What’s Inside the Plastic Shell
The filling in most plastic ice cubes is distilled water, sometimes with a preservative added to prevent bacterial or algal growth inside the sealed cube, and occasionally a thickening agent that gives the liquid a slightly gel-like consistency. These additives are food-grade, meaning they’re approved for contact with things you eat and drink. The water inside freezes at the same temperature as regular tap water and absorbs heat from your beverage as it warms back up.
You may also see reusable ice cubes marketed as “gel-filled.” These typically use a water-based gel rather than a free-flowing liquid. The gel is held together by a thickening agent (often a food-safe polymer or protein network) that traps water in tiny pores. The water still freezes and melts inside those pores, providing the cooling effect, but the gel structure keeps it from sloshing around. Researchers at UC Davis have experimented with gelatin-based hydrogels for this purpose, finding that the water stays locked in place through repeated freeze-thaw cycles without leaking out.
How the Outer Shell Is Made
The plastic casing is typically a polyethylene or similar food-grade plastic. Most brands now advertise their shells as BPA-free, meaning they don’t contain bisphenol A, a chemical that has raised concerns about hormone disruption. Under federal law, any substance intended to contact food, including plastic ice cubes, must be authorized for that use before being sold in the U.S. The FDA evaluates how much of a material could migrate into food or drink and whether that level is safe for consumers.
Stainless steel reusable ice cubes are also available. These contain no liquid at all and cool drinks through the metal itself, which absorbs heat. They’re a different product entirely, but worth knowing about if the plastic shell is your main concern.
What Happens If One Breaks
If a plastic ice cube cracks and leaks into your drink, the exposure is low-risk. The Missouri Poison Center notes that swallowing the liquid may cause a bad taste and minor stomach or mouth irritation, but no serious symptoms are expected from either the water, the preservative, or the thickener. If the liquid gets in your eyes, it can cause immediate burning and stinging that needs to be rinsed out promptly.
The practical advice: if you notice a cube is cracked, cloudy, or leaking, throw it away. A compromised seal also means bacteria from your drinks could get inside the cube, where it’s impossible to clean.
How Well They Actually Cool Drinks
Plastic ice cubes cool drinks noticeably less effectively than regular ice. There are two reasons for this. First, regular ice melts, and that phase change from solid to liquid absorbs a large amount of heat. Plastic ice cubes undergo the same phase change internally, but the plastic shell acts as an insulator, slowing heat transfer. Research on gel-based cooling materials shows they deliver roughly 80% of the cooling capacity of regular ice of the same size.
Second, they work more slowly. In comparative testing, plastic ice cubes took about 22 minutes to bring a drink to their lowest temperature, compared to around 8.5 minutes for regular water ice. Stainless steel cubes fell in between at about 11 minutes. The tradeoff is simple: plastic ice cubes keep your drink from getting watered down, but they won’t get it as cold or cool it as fast.
Keeping Them Clean
Because reusable ice cubes sit in beverages repeatedly, their surfaces can pick up residue, sugars, and bacteria over time. Washing them with warm soapy water after each use and drying them before returning them to the freezer is the simplest way to prevent buildup. Avoid putting them in the dishwasher unless the manufacturer specifically says it’s safe, since high heat can warp or crack the plastic shell.
Inspect your cubes regularly for cracks, discoloration, or a sticky film that doesn’t wash off. With proper care, a set can last through years of freeze-thaw cycles. Once the plastic starts showing wear, replace them. A cracked cube defeats the purpose and introduces hygiene problems you can’t fix by washing the outside.