I did a few tests on this packaging material before, the peanut jar. Leak test, failed. Half-filled the jar with water and shook it. Water droplets were spilling out. It was not conclusive, however, I never used appropriate bottle seal.
Appropriate seal? The jar lid should be sealed using induction sealer with appropriate seal for this plastic. This PET perhaps so the seal should be made specifically for it.
Lukewarm water test. The bottle can hold itself well. Fair enough, barely hot water can never harm human skin, what less to a PET type plastic.
Hot water from a thermos. There was a slight deformation after few minutes. And that modest is unforgivable. It might affect the lid resulting to faulty seal. Disruption to structure might have also caused migration of plastic molecules to contents.
The last was hot water steam test. Held the bottle with the lid facing down the rushing steam. It shrunk so suddenly to unusable state, just like a flattened canned softdrink. It won’t budge if it was heat set.
So I concluded. It cannot be used for hot-packing products, but very much suited if allowed to cool to acceptable level. However, I found something interesting recently. The cocoa nibs that I packed in, tasted and smelled like plastic. It was faint, but may not in senses of sensitive buds. For me, it was awful, masking the original delicate flavors.
I bought samples of this PET jars to package our product cocoa nibs. We ended using the clear stand-up pouches. The latter is cheaper, look as good, easy to seal with impulse sealer and easier to handle.