Foil vs. plastic pouches for seed bank storage
We have used both foil and plastic vacuum sealed pouches for packaging glassine envelopes prior to storage in the seed bank freezer. Are there major advantages to foil vs. plastic? We have used foil historically, but have also used plastic. The benefits to plastic that I see are not just that it is cheaper, but also that you can customize the size of your pouch more easily. Sometimes we have a very small collection and don't need a full foil pouch and sometimes if we have bulky seeds, it's helpful to make a slightly bigger pouch. The biggest difference that I see between the two is the exclusion of light from the foil pouches. I'm interested to hear whether others have thought about this and what conclusions they've come to.
I am so glad you brought this up. I am currently in the process of trying to source some new pouches so this will be very helpful. I'll be interested to see what others have to say about this. I'm also interested in the efficacy of using vacuum sealing as a general practice. Is there any documentation out there about how it compares to traditional (non-vacuum sealing)?
It's been a while since I thought about this, but at some point when we got our foil bags I had done some lookinga round and this is what I'm remembering...
One thing I didn't know going into it was that foil bags are not just foil, they are a mix of layers of plastic and foil, often several layers of varying thickness, not just one of each. A lot of vendors will publish information about exactly what the layers are and even post how much exchange through the barriers there are (for both air and moisture, sometimes even breaking out Oxygen and CO2, I think). The upshot is that foil bags, in addition to providing light protection, also have increased exchange protection (i.e. they allow less exchange of air and moisture). My assumption has been that the better the resistance, the better the storage, and usually that means the thicker the bag (especially the foil layer), the better the resistance. But I've wondered if there is a certain thickness beyond which you are paying for more than what you really need.