What are transparent blocks in Minecraft?

Minecraft's collection of in-game blocks continues to grow, but players are likely aware that blocks also have a wide range of different classifications. This includes the overall opacity of a block and how much light it permits to pass through it, resulting in blocks known simply as transparent blocks capable of allowing light and the appearance of other blocks to render behind them.

Granted, not all transparent blocks in Minecraft work the same way, but they're unified in the fact that they allow blocks to render behind them in the game engine, and many transparent blocks also allow light to pass through them as well.

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Transparent blocks in Minecraft explained

Glass is one of the most commonly known transparent blocks in Minecraft (Image via Mojang)

While one might think that Minecraft's transparent blocks are classified as such because their surfaces allow light to pass through them, things are a bit more complicated. When a block is classified as transparent in the game code, the game engine is notified that it can render blocks behind the transparent ones, which doesn't occur for blocks categorized as opaque.

Transparency doesn't just apply to blocks with see-through surfaces, as blocks that are not considered "full blocks" like slabs, cacti, stairs, chests, and more are also given this classification. As long as the game allows other blocks to render behind a given block, it's considered transparent. The alternative is opaque blocks that will not render blocks behind them in the engine and actively block light.

For example, a block like stone will prevent light from passing through it in Minecraft and players cannot stand and look at the block and see anything rendering behind it. The same can't be said for transparent blocks like glass, ice, leaves, beacons, and more, which can be peered through to see what's on the other side while also allowing light to transfer through their surfaces.

Ice blocks are considered transparent while obsidian blocks are not. Note that the ice allows the obsidian to render on-screen behind it. (Image via Mojang)

While the categorization of transparent blocks encompasses different blocks in the game, some stick to the criteria of rendering and light passage more stringently. As an example, despite being a fully solid block, copper bulbs in Minecraft 1.21 are considered transparent because they allow blocks to render behind them, typically to facilitate redstone signals that can activate them. However, copper bulbs aren't transparent with light the way that glass is.

Regardless, the following blocks are classified as transparent according to the game's code:

Block Type	Blocks
Solid Full Blocks	Barriers Beacons Copper Bulbs Frosted Ice Glass Glowstone Ice Leaves Observers Sea Lanterns
Solid Partial Blocks	Amethyst Buds/Clusters Anvils Azalea Bamboo Beds Bells Big Dripleaf Brewing Stands Bubble Columns Cacti Cakes Calibrated Sculk Sensors Campfires Candles Cauldrons Chains Chests Chorus Flowers Chorus Plants Cobwebs Cocoa Composters Conduits Daylight Detectors Decorated Pots Dirt Paths Doors Dragon Eggs Enchanting Tables End Portal Frames End Rods Ender Chests Farmland Fence Gates Fences Flower Pots Glass Panes Grindstones Hanging Signs (Wall Variant) Honey Blocks Hoppers Iron Bars Ladders Lanterns Lecterns Lightning Rods Lily Pads Mob Heads Moss Carpet Extended Pistons Pitcher Plants (Crop Variant) Pointed Dripstone Redstone Comparators Redstone Repeaters Scaffolding Sculk Sensors Sculk Shriekers Sea Pickles Single Slabs Sniffer Eggs Snow (2-8 Layers) Soul Sand Stairs Extended Sticky Pistons Stonecutters Sweet Berry Bushes Trapdoors Trapped Chests Turtle Eggs Walls
Non-Solid Blocks	Air Banners Buttons Cave Vines Coral Coral Fans Crops Dead Bushes Dead Coral Fans Dead Coral End Gateways End Portals Ferns Fire Flowers Fungi Glow Lichen Grass Hanging Roots Hanging Signs (Ceiling Variant) Kelp Levers Light Blocks Mushrooms Nether Portals Nether Sprouts Nether Wart Pink Petals Pitcher Plants (Non-Crop Variant) Powder Snow Pressure Plates Rails (Including Activator, Detector, Powered Variants) Redstone Dust Redstone Torches Crimson Roots Warped Roots Saplings Sculk Veins Seagrass Signs Small Dripleaf Snow (1 Layer) Soul Torches Spore Blossoms Stems Structure Voids Sugar Cane Torches Tripwire Hooks Tripwires Twisting Vines Vines Weeping Vines
Fluids	Lava, Water
Blocks that Permit Rendering but not Light	Invisible Bedrock, Slime Blocks (Mob Spawning Can Render Behind), Monster Spawners

Put plainly, Minecraft's transparent blocks are a way for the game engine to know what blocks it should place on screen in the player's vision and which to avoid until the player can physically see them. To prevent performance issues on a player's platform of choice, some objects are only rendered in-game when they can be placed in a player's view and not before.

This prevents a player's device from rendering countless blocks they can't see, therefore bogging down the CPU/GPU and likely causing issues like freezing, stuttering, or outright framerate drops. Thanks to the transparency categorization, Mojang's sandbox title stays active and renders important blocks in the scope of a player's vision first to avoid overwhelming the system.