Also - one tip I learned this past week.
Buy the poly-mailer envelopes (they don't rip or tear and are weather resistant). These are lighter than a large envelope and you can fill them with fabric or magazines with added protection against all the elements involved in the delivery process...such as gorillas throwing your package around....package getting ripped apart after being thrown like a frisbee...etc. etc. etc.
First Class Parcel is how they can be sent if they are chubby packages and under a certain weight.