I then placed five frozen bottles into Tesla’s Frunk Cooler and five into Cooler Y at exactly the same time.

The vehicle remained parked outside in Southern California with:

• Same Tesla Model Y

• Same start time

• Same frozen bottles

• Climate Control OFF

• Cabin Overheat Protection OFF

First check — approximately 18 hours

At the first check, one bottle inside Tesla’s Frunk Cooler had already melted completely. The remaining four bottles contained only a small amount of ice.

At the same time, all five bottles inside Cooler Y were still mostly frozen with only limited melting.

Second check — approximately 40 hours

By the second check, all five bottles inside Tesla’s Frunk Cooler were fully melted, and the water was close to ambient temperature.

Why was there a difference?

I think the result mainly came down to two factors:

1. Insulation

After the test, I measured both coolers.

The wall section I measured on Tesla’s Frunk Cooler was approximately 1.5 inches thick.

Cooler Y uses different insulation thicknesses throughout its design:

• Left and right end walls: approximately 4 inches

• Front and rear walls: approximately 2.5 inches

• Lid: approximately 2 inches

The thicker insulation was intentional because our original design goal was up to 7 days of ice retention.

In a separate laboratory-style test at 90°F and 50% relative humidity, Cooler Y retained ice for 7 days.

2. Location

I also think location played a role.

In this parked Tesla Model Y, the rear sub-trunk appeared to provide a more protected environment for passive cooling than the frunk.

An important limitation

This was intentionally a light-load test, not a maximum ice-retention test.

Tesla’s Frunk Cooler has a capacity of approximately 42 QT, while Cooler Y has a capacity of approximately 45 QT.

Five 16.9 oz bottles contain only about 2.65 QT of frozen water. That means the frozen load represented only about 6% of the total cooler capacity in either setup.

A full-capacity ice-retention test would require much more frozen mass. For example, filling about two-thirds of a 45 QT cooler would require roughly 30 QT of ice or frozen contents.

This was also not an insulation-only laboratory comparison, because both the cooler design and the storage location were different.

Instead, it was a real-world comparison of two complete Model Y cooling setups:

• Tesla’s Frunk Cooler in the frunk

• Cooler Y in the rear sub-trunk

Final thoughts

I'm not saying Tesla’s Frunk Cooler is a bad product. It was designed for the frunk and has its own use case.

For camping, groceries, drinks, and road trips, I simply wanted to see how these two complete setups performed in the locations they were designed for.

One unexpected takeaway for me was that frozen water bottles work really well. They stay clean, there's no loose ice water to deal with, and when they finally thaw, you still have cold drinking water.

In this particular 40-hour test, Cooler Y kept the frozen bottles colder for noticeably longer than Tesla’s Frunk Cooler.

Thanks to everyone who shared ideas and challenged the test design. Many of those suggestions helped improve this comparison.