Are 7 Mil Bags Better than 5 Mil?

Ours are, but that's not the whole story.

Random Friday 5 Mil Mylar Musings, episode 3 (yes, I am very strange): As I was reading and responding to one of the threads on Mylar bags yesterday (specifically a comment about very few bags using actual Dupont-Teijin Mylar), something occurred to me. I’ve referenced it previously when I talk about how many companies are now listing bags based on their total thickness, not industry standard Mils Per Side. (I also pondered whether sellers not using actual Mylar in their bags (most of them) should even call their bags Mylar Bags, but that’s not today’s subject!)

So here goes: The thickness of a Mylar bag is just that, a measure of thickness. It is NOT a measure of strength, durability, OTR (oxygen pass through), MVTR (moisture pass through) or any qualitative trait of the bag that actually impacts how long your food will stay good for. Stop and think about that for a minute. Mils and shelf life are not directly correlated. Yes, that is a VERY bold (and perhaps controversial) statement.

Mylar bag thickness is like a person’s height. Neither Mils nor Height measure strength or effectiveness. Yes, it is true that tall people are sometimes strong. But not always. And it is true that high Mil bags are sometimes also strong…but again, not always.

What folks who say ‘You should use 7 mil Mylar’ IMO mean is: ‘you should use high tensile strength, high burst strength and high OTR/MVTR bags.’

When people recommend 7 mil bags, there is some sort of assumption that it must be strong, durable, and have high OTR and MVTR. Many (maybe even most) people buy 7 Mil Mylar bags believing inherently that these things are true. But like the desiccant absorber myth, is it really?

The one engineer on Youtube doing real ASTM testing (Phil@4800) of Mylar bags shows that bags and oxygen absorbers both are all over the board on ‘actual’ strength, and ‘actual’ absorption. There are tens of thousands of people literally buying Mylar bags and oxygen absorbers that are at best average, and at worst suspect, because they have a bazillion 5 star ratings (easily manipulated on Amazon). But no one on Amazon (or off Amazon for that matter) posts sufficient data about their products that actually allow comparison to any other product. Mils is just not, on its own, a sufficient bit of information that an entire community should use to make a decision as important as how to store their food long term.

Why? According to testing, a couple of the most popular brands of oxygen absorbers (Including Wallaby and Amazon FullSeal) have an ‘actual’ rating below their rated capacity (In CC’s), including products regularly mentioned on many Facebook forums and being regularly advertised by influencers and companies on Facebook. Additionally, two very popular 7+ mil brands actually test lower (Harvest Right and Wallaby) than Discount Mylar Bags 5 mil bag in two categories (the third category wasn’t tested for the 5 mil bag). My best guess is that the top bags (ours) still has actual Mylar in them, whereas our competitors are using inferior barrier layers, leading to poor results.

One of the things I talk about with my girls while home schooling is the concept of ‘precision’. When we solve an equation, when we make an argument, when we present a ‘fact’ (‘TS is just the beeeeeeeeeeeeeest daddy, there’s no denying it!!) we should do so being able to provide some support for said thing.

Saying ‘you should store food in 7 mil bags’ is not as precise as saying ‘you should store food in bags that have high tensile strength, excellent burst strength, and great OTR and MVTR) Yeah, that’s way more wordy, but those things are qualitative in a way just Mils are not. Just like there are 5’ people stronger than people that are 6’6”, there are high quality 5 mil bags on the market that are stronger than a couple of their very popular 7 mil competitors. And there are some 7 mil bags that are twice as good (ours) compared to the ‘same’ products, other 7 mil bags.

Anyhow, there’s my ‘too much information’ for the week!