Foil

Foil is a special processing applied to the card, giving them a foil or "glossy" finish over their artwork or entire Card Frame.

Details
It can also refer to the cards that have received this process, also known as "Foil Cards" or "Kira Cards".

In Duel Masters, cards with the Legend Rare, Double Victory, Victory, Super Rare and Very Rare also feature a foil specification. Some promotional cards, as well as Alternate Artwork cards such as Catino Cards, Heroes Cards, Miracle Cards, Mode Change Cards and Dramatic Cards also received the foil process.

Foil cards reflect as various colors when they are exposed to light. Due to this special appearance, many of the main cards of Booster Packs or Theme Decks are featured as foil cards.

However, there is no direct relationship between the strength of the card even if its a foil card at a higher rarity.

About Warpage
Foil cards can suffer from environmental moisture and began to warp. Even if they are put into a card sleeve, they may still be distinguishable from other cards.

In Duel Masters however, cards with the higher rarity are usually only found in a foil spec, and often have powerful cards that are used in the metagame due to their higher card rarity

Efforts should be made to reduce foil cards from warping if the player wishes to attend an official tournament event. Methods such as using desiccants, or leaving heavy objects over a single sleeved card (such as a book) can help this process. Attention should be paid to not damage the card in anyway trying to decrease the warping.

Other

 * There are various forms of foil patterns, which are updated irregularly for different specialty products.
 * Apart from Super Rare and Very Rare foils, cards that have a foiling effect that resembles "scattered broken pieces of glass" are known as "laminate cards". This was featured on multiple promotional cards for the CoroCoro Comic magazine and appendices.
 * Contrary to a foil card, a non-foil card would be known as "normal", with no processing applied whatsoever.
 * Because of the existence of Mode Change Cards and Dramatic Cards, cards are not necessarily more expensive because they are are foil. Card prices are usually only based on the strength of the card itself.
 * Super Decks have a foil specification used on their alternate Card Frames (Silver Frame or Metal Frame. There are 3 patterns of foil used for Super Deck Zero and 1 for Super Deck Cross. After Super Deck Cross, a custom foil to each deck was used and a "Supre Solid Foil" for psychic creatures.
 * [Dash TV] recommends that the warping of cards returns to normal when the card is dried, but cards can lose coloration if left in direct sunlight, or dirty or stolen when left outside.