What kind of processing is the '4 rounds of PU coating' mentioned in the bag description?

When looking through the backpack description, along with basic water resistance, the unfamiliar expression '4 rounds of PU coating' appears. It makes one wonder what role this processing of applying a coating four times to the fabric plays.

hmmm editorial answer

It is a waterproof treatment that applies polyurethane four times to the inside of the fabric to prevent everyday rain or water droplets from easily seeping into the bag.

The number 4 refers to the number of times the waterproof membrane has been layered. PU coating is a processing technique where polyurethane resin is thinly spread on the inside of the fabric to prevent water droplets from seeping between the threads. By repeatedly applying a thin waterproof membrane four times, it achieves basic everyday water resistance to block sudden rain or snow^[1].

The base outer fabric is also tough. RYOO's Symmetric Codura Backpack #2 [black] is made from Invista's Nylon Cordura 750D (Nylon Cordura 750D) fabric^[2]. Cordura is a high-strength textile resistant to abrasion and tearing, widely used in outdoor gear. By adding four layers of urethane membrane to the inside of this sturdy fabric, it is designed to protect belongings inside the bag even in rough weather^[3].

hmmm, rather than decorating the exterior flamboyantly, it is a construction where thin membranes are layered on the inside of the fabric to quietly repel moisture.

Official product page ↗Symmetric Codura Backpack #2 [black]Sold Out

Unanswered questions

Beyond everyday water resistance, the specific water pressure resistance figure that can withstand prolonged exposure to rain has not yet been confirmed.