Yes I realize this is resurrecting a semi-old thread but this information was useful to me and may be to others:
Much of what I have read indicates that O2 permeability is higher with the foodsaver bags as compared to mylar. As has been mentioned mylar also seals out light which is damaging to hops.
In my experience most of the hacks to make mylar bags vacuum seal-able with foodsaver and similar devices do not work very well. As some others have pointed out, while I am able to pull a vacuum on the mylar using "straws" or strips of the foodsaver embossed bags, the sealer does a poor job creating an airtight seal around this and the bags tend to loose their vacuum over a few hours. The models that do not have a locking latch seem to be more flexible with this type of hack.
The best way to use mylar with these types seems to be to use an O2 absorbing packet and create a regular seal.
There is however one company, Sinbo, that makes a type of vacuum sealer called a snorklevac. Instead of the gasketed chamber, there is a metal tongue that extends inside the bag beyond the heating strip to create the vacuum. When the bar on the unit is pressed to seal the bag, the tongue retracts allowing for a good seal. I have read that this is closer to the way industrial units function if they are not of the vacuum-chamber type. This type of sealer does not require the special embossed bags and works great with mylar. It can be purchased on the sorbentsystems website or amazon. There is a slightly newer model that I have seen on amazon with a canister that goes inline with the vacuum line and will trap dust and liquids preventing damage to the motor. It runs about $130. If you truly want to vacseal mylar and are unwilling to shell out major $$ for an industrial unit, this seems like a good way to go. I'm surprised I've seen so few mentions of this product despite references to the sorbentsystems website for bags and O2 absorbers.
Having worked in a retail homebrew shop, I have seen all kinds of hop packaging. Some use mylar bags flushed with N2 and not vaccum sealed. Others vac seal but don't use mylar. The hops we purchased in bulk and broke down into smaller quantities were sold in vacuum sealed mylar. Whatever you do, keep em cold and use within a year! Even in proper packaging, there will be loss of aromatics/changes in hop aroma and flavor.
