Did you start two threads?

https://www.houzz.com/discussions/6402245/what-do-you-put-under-white-cedar-shingles-on-sidewall

Question about Rainslicker

Are you asking about one of the Benjamin Obdyke products?

Rsinslicker is a Benjamin Obdyke product. Curious if that or Felt #30 or Tyvek is better to use under natural white cedar shingle siding

Start with your location or climate and the design of the wall system. Avoid asphalt saturated buildng paper. Benjamin Obdyke no longer makes Rainslicker but for wood shingles they recommend one of their "Slicker Rainscreens": Slicker Classic, Slicker Max or Slicker HP. This stuff changes every couple of years so it's a good idea to call or email them:

(800) 523-5261 techsupport@obdyke.com.

https://benjaminobdyke.com/wp-content/uploads/2022/12/BOI-Catalog_REV4-3-2023-WEB.pdf

The most important consideration is to provide a drainage space behind the shingles. The choice of particular weather-resistive barrier is less important. If I were installing cedar shingles on my home, I'd couple a (properly installed) layer of commercial grade felt with Benjamin Obdyke's slicker classic (and cedar breather for roofs with cedars shingles.)