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How Long Does a Hot Water Bottle Stay Warm?

Updated: Jan 21, 2023

Hot water bottle with thermometer

Hot water bottles (also referred to as hot water bags) are designed to keep you warm in many situations. But how long can they stay warm? Read our insights below!

Thermoplastic (PVC) hot water bottles with a capacity of 2,0 litres stay warm longer than smaller ones with a capacity of 1,2L or 0,8L. You can keep your hot water bottle warm for longer periods by using a cover made of wool, cotton, cashmere, or polyester. If you don’t have a cover, you can use a bath or kitchen towel to wrap around it and trap the heat.

Rubber vs. thermoplastic hot water bottles

Hot water bottles made of PVC, also known as thermoplastic, stay warm longer than those made of rubber. However, they are less durable and have higher chances of leaking and may thus need to be replaced more often. It is important you do not pour boiling water into them as you might damage them.

Hot water bottle warmth with a cover vs. without a cover

Hot water bottle with a wool cover

1. With a cover

Hot water bottles will stay warmer longer if they have a cover.

Different types of covers are available on the market, some are made of wool, cotton, cashmere, or polyester. While wool, cotton, and cashmere covers are more expensive, they will keep your hot water bag warm for longer.

Beyond keeping your hot water bottle warm for longer, using a cover for it is recommended to prevent direct contact with your skin, which can lead to rash and burns, both for adults and children.

Do I have to use a hot water bottle-shaped cover?

You can also use a thick kitchen towel, bath towel, or a sweater to wrap around your hot water bottle and trap the heat. Make sure whichever cloth you use covers the entire bottle. It may not be as effective as a cover designed for a hot water bag, but it will do the trick.

2. Without a cover

Your hot water bottle will not stay warm as long if you don’t use a cover for it. In addition, as explained above, we do not recommend your body have direct contact with a hot water bag without a cover.

If you use a hot water bottle on your body directly, don’t use it for a period longer than 15 minutes.

Pink hot water bottle

Small hot water bottles vs. large hot water bottles

Large hot water bottles

Large or long hot water bottles will stay warm longer than smaller ones. Large hot water bags on the market typically have a capacity of 2,0L and can stay warm between 3 and 6 hours, depending on the quality of the bottle and the cover you use for it.

Small hot water bottles

Hot water bottles are also available in smaller sizes, with capacities of 1,2L or 0,8L. These don’t stay warm as long as hot water bottles do and typically last 2 to 3 hours, also depending on the brand, quality, and cover. Like large hot water bags, covering a small hot water bottle will help preserve heat and keep your item warm longer.

Hot water bottle sizes


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