The slipcovers are not easy to print, because of their size, they won't fit in a Letter or A4 format.

My solution (rather costly) was to use A3+ (13x19 inches) photo paper sheets. In the 19" side, I cut 2 13x8 inches (33x20 cm) stripes, which are long enough for the slipcovers.

I recommend you use the thickest paper you can fin, at least 300g/m², to obtain a rigid enough slipcover.

I'd also recommend great caution if you're using a glossy finish photo paper, because it will easily be smeared when handled, and be very fragile when cut and creased, however the color will look deep and bright on it.