Why do package contents makes mail rates so different, even if weight is similar?


I got a packages from two people today, one containing books and the other not. I know when you send stuff at USPS they ask if it contains media or other contents. Both of my packages today were similar size, from the same (ish) place, on the same day, yet the package with books was under $4 and the lighter one was almost $11. Why is this? If it weighs more or takes up more space, should it matter the contents to calculate the price?

In: Other

there’s a special rate for books called media mail. its cheaper than the regular rate.

but if you are using the same class of service, ie usps priority mail, express mail, flat rate, package, etc whatever. then similar size and similar weight will be similar price. but likely the books were media mail and the other one was priority mail.