Core Series Thermal Performance Heat

At Purepop, we don’t just claim performance — we test it. To validate the heat retention of our thermal flasks, we conducted a controlled experiment designed to replicate everyday use and scientifically measure results.

Objective

According to international standards, a high-performing thermal flask should keep liquid above 60 °C after 6 hours. Our Core Series flasks go far beyond that, holding heat for a full 12 hours while still staying above 60 °C.

The goal of our test was simple: to measure how well a Purepop Core Series flask can retain heat over a 12-hour period, starting with near-boiling water. This allows us to compare our results not only to industry standards but also to the real-world conditions our customers use their flasks in every day.

How We Tested It

To make sure the test was fair and accurate, we set it up like this:

  • We boiled water to 99.5 °C and poured it into a Core Series flask.
  • The flask was kept in a room at a steady 22.2 °C (no sunlight, no heaters).
  • We sealed the lid tight and left it untouched, just as you would if you filled your flask in the morning.
  • Temperatures were measured at 1, 3, 6, and 12 hours using a calibrated thermometer.

Results at a Glance

1 hour – 94.5 °C → Near boiling, far too hot to drink immediately.

3 hours – 88.2 °C → Similar to freshly brewed coffee.

6 hours – 80.1 °C → Hotter than a typical café latte.

12 hours – 66.8 °C → Still steaming, perfect for tea.

Compare this to an open cup of water, which drops to just 25 °C after only 2 hours.

Analysis

In our controlled test, the Purepop Core Series flask started at 98.5 °C and after 12 hours still measured a steaming 66.8 °C.

When used as intended — with the flask filled and the beverage heated to near boiling — a Purepop Core Series flask is expected to keep drinks above 60 °C for at least 12 hours.

Disclaimer: Actual heat retention performance may vary and is influenced by multiple factors, including but not limited to the liquid’s initial temperature, the volume contained within the flask, external ambient conditions, frequency of opening, and the heating method employed (e.g., kettle versus coffee machine). The results provided are derived from controlled testing conditions and are intended solely as a benchmark reference, consistent with industry practice for premium thermal flasks. They do not constitute a guarantee of performance under all conditions.

Frequently Asked Questions

Why is my flask not holding heat as long as expected?

There are several factors that affect heat retention:

Filling level: A half-full flask cools faster due to the air gap inside.
Starting temperature: If your kettle or coffee machine doesn’t reach a full boil, the drink will cool sooner.
External conditions: Cold environments draw heat out faster than room temperature conditions.
Preheating: Warming your flask with hot water before filling improves retention.
Usage: Opening the lid frequently releases heat.

Even with these variations, your Purepop flask should keep drinks hot for many hours.

How do I test my flask’s insulation?

To check your flask’s insulation, follow these steps:

  1. Boil water and fill the flask about 90% full. Note that some kettles only boil water to 90c.
  2. Measure the starting temperature with a kitchen thermometer (should be close to 98–100 °C).
  3. Seal the lid tightly and leave the flask at room temperature without opening it.
  4. Re-measure after 6–12 hours. A properly insulated Purepop flask should still be above 60 °C after 12 hours.

If the water cools rapidly (e.g., lukewarm after a 3 hours), the vacuum seal may be compromised.

Why does my flask feel warm on the outside?

Purepop flasks are double-walled and vacuum insulated. If the outside feels noticeably warm (or cold), this may indicate:

The flask is extremely full and direct contact is transferring some heat.

The lid may not be fully sealed.

Rarely, it could mean a vacuum seal issue — in which case, contact us for support.

What are signs my insulation is faulty?

The outside of the flask feels hot or cold to the touch (the vacuum layer should prevent this).

Drinks cool down to room temperature within a 2-3 hours.

You hear a rattling sound inside, which can indicate a broken vacuum seal.

Will my flask keep drinks cold too?

Yes! Just as it retains heat, the vacuum insulation keeps cold drinks chilled for up to 18 hours. For best results, add crushed ice.