From PLAYERUNKNOWN'S BATTLEGROUNDS Wiki
BATTLEGROUNDS has special crates that can be acquired via in-game currency or on the Steam Community Market..
Purchasable crates w/ in-game BP -
Purchasable crates w/ in-game BP + Keys -
Purchasable crates w/ in-game Steam Marketplace + Keys -
Purchasable crates on Steam Marketplace only -
Discontinued crates -
- Q: What economy system is used in PUBG?
A: "Our in game currency/points system is known as Battle Points (BP) which is used to open crates. They grant players one random cosmetic item which they can trade on the Steam marketplace, deconstruct for currency or equip on their character." 
- Q: Why do BP crates cost more the more you buy?
A: The reason crates get more expensive the more you buy is to enforce a soft limit on the number of crates you can buy a week. This creates an economy based on our skins. Limiting the number of crates you can obtain a week is important to make sure there is rarity within items so there’s value in the marketplace.
- Q: Will you be adding Pay To Win elements to the game?
- Q: Do I keep these items after the official launch (after Early Access) of the game?
A: Yes, you will keep all items that remain in your inventory even after the official launch of the game.