What is the best size for a direct mail piece?

There are no rules about what is the best size of a direct mail piece - and the more unusual the size the more likely the reader is to take notice - but remember these facts.

The normal sizes for direct mail are 

Certainly it is not worth sending two or three A4 sheets flat - they will simply get crumpled in the post.   What you should consider, if you have a small number of A4 sheets is folding them in half and putting them in a C5. 

Up to 100g A5 items can cost less than A4 mailings.

How many items should you put in a mailing?

Much depends on the type of message and the people you are trying reach.   Three or four pages is quite normal, as is the standard catalogue plus cover letter, or the brochure (again with the cover letter.)   

But there is no rule that says you can't send 8 pieces of paper - or indeed 8 pieces of paper of different sizes.  In the end everything comes down to the simple question - does it work or not?

But do take care.  There is a phenomena in direct mail called "interference".  In short this is what you find...

a) You mail (say) two leaflets advertising a book or a series, and get a very satisfactory 4% response rate.

b) Next time you repeat the process but add a third leaflet.   Sales collapse to zero.

The explanation is interference - the first two leaflets work -but not in the presence of the third.  

It's complex stuff, and if you really want to get into it, you need to read what is said in www.mailing.org.uk.  Or alternatively call 01536 399 00 and have a chat.