Posters can be:
Your advisor is resonsible for cover the cost of poster production. (So that may impact the kind of poster you make.)
The posters can be any size you want. So, if you or your group might use this poster for other purposes (such as a conference), then you can go by those requirements and 'reuse' your poster for the Forum.
But if you are making it specifically for the Forum, these are the typical sizes:
Posters can even be larger, but the 24"x36" version is the most common at the ISR Forum.
ISR has foam boards that can be re-used if you make a roll up poster and attach it to the foam board. ISR will provide black clips and push pins. If you use an ISR foam board, you should not use any other means to attach your poster to the foam board (tape and glue damage the poster boards). ISR's foam boards are 24"x35" and 30"x40". A roll-up laminated poster doesn't have to match that size perfectly - it's ok if it hangs over the edges a bit.
You are welcome to come and look at some of the posters that we have from prior years, to see what they look like.
ISR will provide easels which you can rest your poster board on (i.e. they do not have clips at the top). The easels stand on the floor, or can be shortened and put on a table if you need a table, e.g. if you plan to also do a demo.