Going Beyond Areal Density in Balloon Film

I received two sets of 10 x 60" "Cymylar" balloons purchased from Yiwu Creative Balloon on the Alibaba site. I paid $62.68 including shipping, import charges, and sales tax, averaging out to $3.13/balloon.

Ordered the day after Christmas, they arrived on January 11th, just over 2 weeks after I paid for 'em.

I immediately cut the first balloon into 20 cm x 20 cm squares in order to satisfy the first of many burning questions.

What is the areal density of these party balloons?

Now, you can get super fancy on this measurement, but we don't need to dive into equipment that costs more than a hipster's monthly coffee allowance. Yet.

Cut up enough squares of a known area, fold 'em all up and secure it with tape (remember to tare out the tape!), weigh 'em, then divide the total mass by total area and you get 28.33 g/m².

Estimating Film Thickness from Areal Density

Areal density can be converted to thickness if we assume a material density. Of course, we have to know what the material is first, and this particular manufacturer didn't include a datasheet with the balloon, so I did a few kitchen tests.

Kitchen Testing Balloon Film

The following are informal versions of far stricter testing methods. I used what was at hand to get a baseline idea of what this envelope is.

Tensile Pull Test: I cut out a strip 20 cm x 2 cm and did a pull test; it snapped at about 20% elongation.

I did the same thing with a wider piece, 10 cm x 6 cm, and it went from 10 cm to 12 cm before snapping; about the same.

Before pulling, the sides on that thin strip curled up rapidly, indicating an oriented film.

Tear Propagation Test: I made a small cut in one edge of a strip and hand-tore it; it tore straight, with no wandering. This also indicates an oriented film.

Float-Sink Density Test: Fully wetted, the film sinks in water. PET tends to sink, polyolefins tend to float. By this time I'm pretty sure this is some kind of PET.

Hot-Needle Puncture Test: A heated needle passes easily through it and creates a wide hole.

Heat-Shrink Test: Brief exposure to an open flame caused rapid shrinkage followed by stiffening and increased crinkling, behavior consistent with oriented PET films and inconsistent with ductile polyolefins.

While none of these are definitive, they all point toward a highly oriented PET or PET laminate.

With PET as the working assumption, we can turn areal density into thickness.

Back to the density question

As the nerds say, definitive identification would require FTIR or DSC. For first-pass envelope trade studies I'm pretty happy with calling this a PET or PET derivative.

Using a PET density of ~1.38 g/cm³, thickness follows directly from the measured areal density:

28.33 g/m² → 0.002833 g/cm²

Thickness ≈ 0.002833 / 1.38 ≈ 20.5 µm

While the vendor markets these balloons as “Cymylar / Mylar,” the kitchen tests point strongly toward a highly oriented PET or PET-dominant laminate.

That puts this material squarely in the category of thin, low-cost, dimensionally stable films—excellent for experimentation, iteration, and early learning.

And that’s exactly where these balloons shine.

Field data backs this up. Across a large set of flights, outcomes break down roughly as follows:

Duration band	Share of flights	Count
< 2 days	6%	28
2–7 days	29%	125
7–30 days	35%	151
> 30 days	30%	131

In other words, roughly 70% of flights experience all-cause mortality within the first month, and nearly a third don’t survive the first week.

Now, I'm not saying this material is bad. It's awesome for what is, and extraordinary compared to its original design intent.

Thin, economical, oriented PET films are optimized for availability and cost, not long-duration exposure to UV, thermal cycling, creep, or micrometeoroid-level damage.

So this balloon film is an excellent place to start:

• cheap

• accessible

• consistent

• easy to characterize

But it’s not where we'll finish.

Once the goal shifts from learning how balloons behave to engineering envelopes that last, these same measurements — areal density, thickness, orientation, and failure modes — become the baseline against which more durable materials can justify their mass and cost.

Onwards!