I'm just wondering if I use a padded envelope to mail a book can I still print my postage off this site? Will the postage amount still be correct or does using a padded envelope increase the cost of postage? 

The price of postage depends on the weight, so yes, a padded mailer could increase the weight and thus the postage required.

If you are going to use a padded mailer, make sure it's folded down tight around the book. If the book shifts around in the mailer, it has a very good chance of ripping out of the mailer and becoming lost.

Echoing Brady's comment.  Every single damaged package I've received has been envelopes (padded or plain manilla) that are not tight around the book.  An edge or corner gets caught and torn.  Luckily, I haven't had any books lost or damaged beyond postability rules, but it's probably only a matter of time.

Stacy, If you are using printed postage from this site, I'd strongly urge you to use a scale and weigh your wrapped packages before printing the postage - then correct the weight shown to ensure you have correct postage. The weights on this site are estimates only, and not checkingthem may lead to the wrong postage being on your parcel -either it may arrive postage due, or, you may overpay.

no matter what package you mail it, its is WELL worth your while to get a postal scale.  The weights in PBS can be incoffect.

I use PBS postage and padded (bubble) mailers when I mail.  I agree with everyone else's advice to get a postal scale.  The padded mailers do add a few fractions of an ounce to the weight, and that can sometimes shift the price of the postage up to the next level.  Also, there have been many times when the PBS weight was just wrong to begin with.

As far as printing out the label, there is an option to print a single page (or even a sticker).  The label prints out with the requestor information on the bottom 1/2 of the page.  I just cut out the actual mailing label (conveniently outlined in a box) and stick the bottom of the page in the package with the book.  I find it much easier to handle that vs. the two page wrapper.  1--I'm a terrible wrapper and always end up with a paper/tape mess if I use that method.  And 2--I'm just too lazy to have to go through all that.  I figure what I save in paper and ink, I can spend the extra on the mailers.  And you can usually get deals on them somewhere on line.