5 Mil vs. 7 Mil…again.
Back in the old days, I used to love getting into a good ole’ Facebook (or forums before that) row. Nowadays, it makes me sick to my stomach. As a father, I try to give good advice to my daughters; a consequence has been I try to take any advice that I give them (ugg!). Kindness, forgiveness, sharing, compassion etc. I really struggled with that last night.=)
I basically had a Facebook person telling me that I was lying when I said you could store food long term in 5 mil bags, and that I was a horrendous person trying to kill people because I had too many 5 mil bags on hand I couldn’t get rid of. Of course, most of us know you can store food in 5 mil bags because we’ve done it; I even have food from 2007 still stored in 3.5 mil and 4.3 mil bags. These products have been around for decades, and if they DIDN’T work, we’d know it. The Internets would be full of stories of failed bags and ruined food. And yeah, occasionally one of those stories pop up, and the culprit is usually user error. I had my own share of failures back almost 20 years ago when I first started and I didn’t know what I didn’t know; but again, that was on me, and not on the products involved. The good news is we also see the stories about folks opening up their Y2K food in 4.3 mil bags and its all still awesome.
So today, I’m going to break down the argument that there is something intrinsically better about a 7 mil bag that makes it so superior that 5 mil bags should never be used. You can find lots of this info in our video here, I’m just going to go into a bit more detail in this post.
Let me start with some premises:
1: Yes, the best 7 mil bags will be better than the best 5 mil bags. I think this is where some of this argument stems from. A good manufacturer of bags cares about both their products and the materials they are made from, and so our 7 mil bags are ‘better’ than our 5 mil bags from a technical standpoint, because there’s more quality material there. As examples, we add Nylon for tensile strength, we use real Mylar because its inherently stronger than the materials people replace it with. These things make a difference, and the testing shows it.
However, here’s the rub. Just because the 7 mil bag is ‘better’ by a few percentage points doesn’t mean its going to keep your food fresh any longer, because the amount of oxygen and moisture getting to your food is so small due to the incredible barrier properties of the primary barrier layer, which isn’t actually Mylar…its aluminum foil.
The harder truth for some folks to realize is that there are some 5 mil bags that are measurably better on some performance indicators than some 7 mil bags, depending on who is making the bag. It’s like how you can have a $25,000 automobile with better acceleration than a $40,000 automobile.
2: Aluminum foil – The best Mylar bags (4.3 mil and up usually) on the market use a .00035″ layer of aluminum foil (some also use a thinner .000285″ layer). It’s a common laminate, and used in all kinds of things, from reflective insulation to metallic tape. And in perfect condition, it has zero oxygen and zero moisture pass-through. This is the main reason why 5 mil bags have nearly identical barrier properties to 7 mil bags…they are both starting from a base of zero. Now, there is a measurement regarding the aluminum foil layer, ‘pinholes per meter squared’, and this is why when in actual use Mylar bags don’t have perfect scores when it comes to oxygen and moisture penetration. Both in the manufacturing process, as well as in the process of storing food, it has and can develop tiny pinholes. In many places on the Internet, you can see people freaking out about pinholes…but they are just part of the process, and they are inevitable. And this is why your Mylar bags have several other layers that are NOT prone to pinholes.
3: Other Layers – In our case, our 5 mil bags are made of 5 total layers, and our 7 mil bags have 7 total layers. We are the only Mylar bag seller we know still using Mylar as one of those layers. So why Mylar? It has good barrier qualities, exceptional tensile and mechanical strength and is very easy to work with. Others replace Mylar with lower-performing materials because it is expensive. LLDPE, the most common replacement for Mylar used by some of our competitors, is up to 500 times worse (yes, the numbers can be crazy) on OTR (Oxygen transmission) and up to 10 times worse on WVTR (Water vapor transmission) than actual BoPet. Our 7 mil bags (and now our Steelpak 4 mil bags) have a Nylon layer. Why? Because it too offers added puncture protection.
Most sellers sell 3-4 layer bags because they are cheaper to produce and offer sufficient protection for many uses. The good part for them is that a thick bag feels like a thick bag, however its made, which is why when you ask ‘what’s your favorite Mylar bag’ you get so many answers, because they all FEEL good and sturdy, and most folks think that correlates to being made from quality materials. However, ask other producers what their bags are made of, and WHY, and you’ll likely be greeted by blank stares. Most other sellers are white labelers, meaning they create an e-commerce business around selling a product that’s profitable. And there’s nothing wrong with that. But they are not Flexible Packaging companies, of which Discount Mylar Bags is the only one specializing in food storage packaging solutions. Even though most folks know us as Discount Mylar Bags, our official name is ShieldPro Flexible Packaging, because we design packaging solutions for both the retail and corporate marketplace. Our customers range from the Department of Defense, Oak Ridge National Laboratories, multiple university research labs (One which said our bags tested better for pharmaceuticals than some products designed for it), multiple food and supplement companies, the USAF (to protect parts from corrosion) and hundreds of others.
4: The Science – I know, I am very skeptical of that term as well. However, in this case, it is just the measurement of how products perform. I’m not even going to use the fancy OTR/WVTR numbers (though you are welcome to email me about them)…I’m going to break it down even further. So how much oxygen does a Mylar bag let through each year?
For a quality 5 mil 1.25 quart bag, the answer is .22cc/year.
For a quality 7 mil 1.25 quart bag, the answer is .19cc/year.
Both of those numbers are ridiculously low. If you are using a 300cc oxygen absorber from us, with around an 1100cc actual rating, and you assume 300cc of that capacity is used when you first seal the bag, you will have enough oxygen absorption for another 3,636 years with a 5 mil bag, and another 4,210 years with a 7 mil bag. So yes, that 7 mil bag will do better for you if you are an Egyptian pharaoh, but not so much if you’re a rural mom or dad like me.=) Of course, your food will break down long before you open the bag, but at least there still won’t be any oxygen in it a couple of centuries from now.
The numbers for moisture are actually closer than they are for Oxygen, and are essentially a rounding error, with no measurable improvement in MVTR between 5 and 7 mil and between .19 and .22cc/year.
So assuming you are using good bags, and good oxygen absorbers, you will get exactly the same results (unless you live 4000 years) using 5 mil bags instead of 7 mil.
I know this post and others like it can make folks feel a little weird. After all, the ‘Internet’ tells me to only use 7 mil bags! And the Internet is never wrong, right?
5: Yes, it feels WEIRD to think a great thick bag isn’t protecting your food much better than a thinner one, but it is true. Take a look at the below chart; these are various types of films used in various products. Please note the HUGE variations in these numbers, a difference by a factor of over 100,000 between some of the products. What films you use in manufacturing matters. However, please note that EVERY one of these films has its place, depending on the application. Some have a better melting point, some are easier to laminate, some bind better to aluminum or another material, etc. But the statement made to me last night, that a 5mil bag CAN’T ever be used to store food long term and that I must be trying to kill people by selling them, is just a statement made from a lack of information.
One type of plastic at 2 mil might not be able to hold up a 12oz cup of coffee, while another 2 mil film of a different plastic might hold up a brick. That’s how big a variation there can be. A plastic bag you put in your fridge might have an oxygen pass-through rate of 1000cc/day. A better one that is lighter than the first might have an OTR rate of 100cc/day, just through the use of different materials.
So if you’ve had a bad experience with a particular bag, please don’t make the assumption that every other product like it will also be bad. There’s as much difference in Mylar bags as there is between a Chevy and a Toyota in terms of quality of materials. And so just because your Ford broke down that time doesn’t mean even every Ford will, let alone another brand.
6: The one actual benefit of a good 7 mil bag: tensile strength and the ability to resist punctures. Yes, if you have puncture prone food, by all means use a 7 mil bag. But if you are only worried about longevity, you can’t go wrong with a 5 mil bag produced by a manufacturer who cares about a quality product, and there are several on the market.
