"R" is a panchromatic paper designed for photo booth, converted and perforated to be used in classic 135 cameras. Processed in specific reversal chemistry it gives a 35mm perforated stripe with small 24x36mm positive pictures, for example the MFS b/w reversal kit available here: http://www.decisivemoment.com.au/mfs-b-w-reversal-kit-1l/
Film is in ISO 100, with 24 exposures.
Please check out the Data sheet here for more information: https://filmwashi.com/datasheet/R100_en.pdf