diff --git a/src/block/Flowable.php b/src/block/Flowable.php
index c3d6f3eb5..2b4e8a02b 100644
--- a/src/block/Flowable.php
+++ b/src/block/Flowable.php
@@ -26,6 +26,10 @@ namespace pocketmine\block;
 use pocketmine\block\utils\SupportType;
 use pocketmine\math\AxisAlignedBB;
 
+/**
+ * "Flowable" blocks are destroyed if water flows into the same space as the block. These blocks usually don't have any
+ * collision boxes, and can't provide support for other blocks.
+ */
 abstract class Flowable extends Transparent{
 
 	public function canBeFlowedInto() : bool{
diff --git a/src/block/Opaque.php b/src/block/Opaque.php
index 43e4e95d6..c699bc258 100644
--- a/src/block/Opaque.php
+++ b/src/block/Opaque.php
@@ -23,6 +23,10 @@ declare(strict_types=1);
 
 namespace pocketmine\block;
 
+/**
+ * Opaque blocks do not allow light to pass through. They are usually collidable full-cube blocks.
+ * Most blocks in Minecraft fall into this category.
+ */
 class Opaque extends Block{
 
 	public function isSolid() : bool{
diff --git a/src/block/Thin.php b/src/block/Thin.php
index ad5824494..f6e41d43a 100644
--- a/src/block/Thin.php
+++ b/src/block/Thin.php
@@ -29,6 +29,9 @@ use pocketmine\math\AxisAlignedBB;
 use pocketmine\math\Facing;
 use function count;
 
+/**
+ * Thin blocks behave like glass panes. They connect to full-cube blocks horizontally adjacent to them if possible.
+ */
 class Thin extends Transparent{
 	/** @var bool[] facing => dummy */
 	protected array $connections = [];
diff --git a/src/block/Transparent.php b/src/block/Transparent.php
index b4489cebf..e1ad9588a 100644
--- a/src/block/Transparent.php
+++ b/src/block/Transparent.php
@@ -23,6 +23,12 @@ declare(strict_types=1);
 
 namespace pocketmine\block;
 
+/**
+ * Transparent blocks do not block any light from propagating through them.
+ *
+ * Note: This does **not** imply that the block is **visually** transparent. For example, chests allow light to pass
+ * through, but the player cannot see through them except at the edges.
+ */
 class Transparent extends Block{
 
 	public function isTransparent() : bool{
diff --git a/src/block/UnknownBlock.php b/src/block/UnknownBlock.php
index 81a2af259..e81e0ed19 100644
--- a/src/block/UnknownBlock.php
+++ b/src/block/UnknownBlock.php
@@ -25,6 +25,9 @@ namespace pocketmine\block;
 
 use pocketmine\item\Item;
 
+/**
+ * Represents a block which is unrecognized or not implemented.
+ */
 class UnknownBlock extends Transparent{
 
 	public function __construct(BlockIdentifier $idInfo, BlockBreakInfo $breakInfo){