Don't buy "buffered" mats. All that means is that there is an alkaline buffer in the paper that helps to neutralize the acids from the wood pulp. Of course, when the buffer is used up, any acid left over can still affect your print. This can happen in as little as 3 to 4 years.
Open your wallet a bit more and buy acid free, rag mats to use as a backer board. You should be using only rag mats for the top mat also.
One of the biggest no-nos I see in my store is a customer comes in with a print they bought and the artist has used the cheapest junk they can find to mat and mount. Of course, some customers insist that I use what the artist put on it because, after all, they are the artist! Surely, they know what's best for their art! Right?
Rarely!
Oh, and please... stop using all manner of tape to attach the image to the back of the mat! That includes not using Duct tape!! First, do not attach the art to the back of the mat! This is the surest way to damage the print when someone opens the package and lifts the mat only to tear the print. Always attach it to the rag backer board or to the rag coated, acid free foam core. Also do not tape the piece all the way around. This only makes the paper ripple into the center as there is no where else for it to go when it expands from temp/humidity. Only hinge it from the top about 1/4 the way from each end.
If all this costs you $20 more in materials, then you just increase the selling price $40.
Seriously, $40 more will not chase customers away.
When the customer sees that you are serious about displaying your art, they will be more willing to pay more for it.
I just had to rant a bit about one of my pet peeves. Thanks.
By the way... you can use Corplast behind the rag backer board to stiffen the package. It is archival and will not damage the art in any way.
Ok. now I'm done.
