A sleeping pack is a semi-occlusive that people may choose to put on as their "last skincare product" before they go to sleep.
As for pigmentation scientific papers say: vitamin c, arbutin (hydroquinone derivative), hydroquinone (USA regulates this as a drug so you need a prescription), alpha hydroxy acids (AHA), and niacinamide. From experience licorce, and willow bark extracts also give me this effect. I am having great effects with andalou naturals tumeric + c enlighten serum ($16 on amazon).
My pigmentation is sun-damage and all the "whitening" products is not skin bleaching but more like... trying to reverse sun damage and put your skin back to what it's tone was pre-sun damage.
People on www.reddit.com/r/asianbeauty <= the largest English community for Asian beauty products; have said they have success with this Scinic Honey All-in-One ampoule. I think because of the niacinamide (scientific papers say a maximum of 4% is effective). I personally use this "sleeping pack products" as a lazy 1 step. I put on some toner because I like toner and then this "sleeping pack." Sleeping packs I tried and liked A LOT are the mamonde rose honey (discontinued) and a close one I found was the "mediheal petalpoten hydrop essential rose mask." These products taught me I like gel textures. Someone enabled me to buy the Scinic Iceland Water All-in-One ampoule. Another one I liked using was the Vichy Thermalia Aqua Night Spa (yes this was #1 ranked in Hong Kong and sold at CVS for $28 dollars when not on sale). However it has fragrance pretty high up on its ingredients list and has some dyes, so I would not recommend for particularly sensitive skin. It's occlusive properties were meh. It feels like some gel texture, but is okay at hydration. It is a WONDERFUL neck cream.
The product I am trying to get for hyperpigmentation, the Gowoonsaesang Dr. G Hydra-brightening capsule serum is not carried by yesstyle. I'm trying to get a buying service to get it for me. It is also sold at Nordstrom for too much money. BTW I still did not get my yesstyle voucher! @jimmy_l Could you update us on the IDs that did not receive this email?