Asgard shield

Asgard shields are the primary defensive technology used by Asgard starships, and are among the most advanced shields known to exist. The technology was shared by the Asgard with the Tau'ri after their contributions in defeating the Replicators and equipped on the Earth-designed Prometheus and Daedalus-class battlecruisers, giving them a great advantage over the space-faring races of both the Milky Way and Pegasus galaxies.

Functions
Asgard shields create an elliptical "bubble" around the starship they are equipped to that absorbs and diffuses the energy from weapons fire. The shields will gradually weaken under sustained fire (rather quickly if the attack is of sufficient force), allowing energy from attacks to bleed through and cause damage to the ship. Although additional energy can be allocated to the shield bubble to reinforce it, the only way for a ship to ultimately survive a continual attack is to withdraw and give the shield generators time to recharge.

Asgard shields are far more effective than Goa'uld shields, and in their more advanced incarnations even most Lantean shields, but they become less effective when facing foes of a comparable technological level. The exact strength of these shields is relative to the power channeled into them, meaning the shields on Asgard starships are more powerful than those of Tau'ri starships unless a ZPM is interfaced, which may even render them more powerful than on Asgard ships. The most advanced shields developed by the Asgard were equipped on the Odyssey before they committed mass suicide, allowing the ship to survive multiple hits from the central weapons of multiple Ori motherships, which no other shield until then has been capable of doing. Although this could be due to the extra power produced by the Odyssey onboard ZPM.

Asgard shields are also one of the few types of shields capable of resisting direct penetration from Asuran drone weapons (the others being Ancient, Traveler, and possibly Ori); however Todd remarked that it would only take one of Atlantis's drones to disable the Daedalus' hyperdrive, implying that the newer and likely more advanced Ancient drones on Atlantis are somehow able to penetrate Asgard shields without much resistance (although he could have just been underestimating the shield's capabilities).