Semtex

Semtex is a type of grenade that sticks to the first surface it touches, including other players, featured in Call of Duty: Modern Warfare 2 and Call of Duty: Black Ops.

Call of Duty: Modern Warfare 2
While the Semtex is not seen in the Campaign, it is featured in both Multiplayer and Special Ops.

Multiplayer
Semtex takes up the equipment slot. It is comparable to the standard grenade but with some differences. It has a set timer and cannot be cooked, though the timer is shorter than a frag grenade's fuse. At close range, the delayed explosion gives opponents time to escape. However, the timer counts down while the Semtex is in flight and will explode almost immediately after landing if thrown over long distances. It has a blinking red light and beeps softly, making it easier to spot and avoid. This makes it useful for flushing enemies that have bunkered down, as they may run from cover if a Semtex charge is tossed in proximity, and if they do not run fast enough, they will be killed or severely injured. Because the grenade sticks to the first surface it touches (except glass, which shatters while the semtex's trajectory remains unaffected), it will not bounce and roll past the desired target. This is very useful for accurately sticking the grenade to the Headquarters, narrow platforms, or hillsides. Additionally, it can be stuck to the window sill in front of an enemy rather than actually requiring the grenade go through the window (a throw which, if missed, often means a cooked grenade comes bouncing back at the thrower.) Additionally, Semtex grenades cannot be thrown back at the original sender.

Semtex is more powerful than a Frag Grenade: it has a larger explosive radius and the highest explosive damage of any equipment in the game. It is the only grenade that can, without Danger Close, destroy the large gas tanks found in Highrise, Overgrown, and Terminal. Unlike the frag grenade, Semtex cannot be overcooked though sticking a Semtex too close will still cause a suicide.

Due to its stickiness, it is very useful for taking down Riot Shields, which it attaches itself to. However, if the shield user has Blast Shield they may survive even a direct stick to the shield.

Less frequently some people will stick Semtex to a team-mate and have them run into a group of enemies - mainly for the "The Resourceful" challenge, in an attempt to kill at least one or two enemies. This works best in Domination or Headquarters, where larger groups of enemies will likely be trying to capture an objective. It is not recommended to try this in Hardcore modes, where friendly fire may kill teammates in the process.

The explosive power and blast radius of Semtex also make it useful for rushing classes because it can clear larger areas than a frag grenade and does not ever require cooking.

Since Semtex cannot be cooked to detonate sooner, it is advised to arc the throw upward if possible. This will allow the explosive to still reach its target, but detonate sooner relative to the enemies noticing. Consequently, the enemies will have less time to react and are more likely to be killed if the throw was accurate.

Call of Duty: Black Ops
The Semtex will return to Call of Duty: Black Ops.

It is seen in the Multiplayer Reveal Trailer and in the Create-A-Class menu which was revealed in the September 1st multiplayer reveal.

Trivia

 * If the player knifes an enemy who is holding out their Semtex ready to throw it, there is a chance of it sticking to the killer with no warning thus killing him.
 * If a player gets Semtex stuck on their Riot Shield, it will always kill the user. The only way to survive it to swap out the shield for a weapon on the ground, or by using the Blast Shield.
 * It is possible to survive being stuck with a Semtex. If the player is stuck on the head or the arms, pushing his head "through" or into a wall and putting the Semtex "through" it will result in the grenade simply disappearing instead of exploding. It is possible to get stuck on the stomach survive the explosion by going prone and putting the Semtex "in" in the floor.
 * It is possible to stick Semtex to any kind of aircraft, except for the high-altitude AC-130 and UAVs.
 * As many people complained about the frag grenade's power in Call of Duty 4: Modern Warfare, it was weakened in Call of Duty: Modern Warfare 2. However, the problem still exists with the introduction of Semtex, which is essentially the same thing as a Call of Duty 4: Modern Warfare Frag grenade, except with the ability to stick. For this reason, frag grenades are seldom used in Call of Duty: Modern Warfare 2 in favor of Semtex.
 * If a player is stuck with a Semtex and they kill the player who stuck them it will count as a "payback" kill.
 * Sticking Semtex to an enemy with Painkiller active will not kill them, except in Hardcore game modes.
 * Semtex replaces flashbangs in some Special Ops missions.
 * In Hardcore modes, a direct hit with Semtex to the groin will kill an enemy player.
 * It appears to make a return to Call of Duty: Black Ops, as seen in the multiplayer teaser trailer.
 * The throwing animation for the semtex in Call of Duty: Black Ops is nearly identical to the one in Call of Duty: Modern Warfare 2.
 * The semtex in Call of Duty: Black Ops blinks green instead of red when thrown.This may be to show it's friendly.
 * It is odd that the semtex is not cookable for when the player pulls the pin the fuse does not start until the grenade is thrown.