adelorenzo, Yupo won't work w/o a primer, it's absolutely impermeable and with cyanotype you need the emulsion IN the paper.

kevin, try Masa paper it's perfect for all iron / iron-silver processes and it's cheap too. (Something like USD 1.2 - 1.3 per 21x31" sheet... I remember the times when it was only USD 0.7/sheet.)