Founded in 1915 as a manufacturer of heating products, Kirishi Chemical is the largest manufacturer of disposable heating products in Japan, mainly selling refrigerants, insect repellents, foot care products, etc. In 2001, Kobayashi Pharmaceutical acquired Tung Ash Chemical, and continued to sell warm patches in Japan under the brand name of Tung Ash, with a market share of nearly 30% in Japan, and is one of the best-selling warm patch brands in Japan.
 
Tung Gray's Spring (はる) series of warm stickers has been on sale since 1988, and its iconic golden packaging is printed with a cute white rabbit, so it is affectionately known as the "Golden Rabbit" brand by consumers, and Kobayashi Pharmaceutical has also named its version of the warm patches sold in Hong Kong directly as "Little White Rabbit Warm Pack", both of which are made in Japan.
 
The average temperature of the regular size of the spring warm paste can reach 53 °C, which can last for 14 hours, and the mini size continues to heat for 10 hours, which is longer than the heating time of Kobayashi warm baby, about 4 yuan per piece, which is one of the most expensive warm patches on the market. Black Spring (黒いはる) is a product designed to match black clothing, the raw material bag and adhesive are black, more suitable for wearing thin formal clothes to keep warm, to avoid the embarrassment of exposing white warm stickers, but in addition to the packaging changed to black, other parameters are no different from the basic version, but the price is more expensive than the basic version, about 5 yuan per piece, black warm paste is now not an exclusive product of tung gray, many brands also have more affordable products for sale.
 
What is more distinctive about tung gray is its various special foot warm patches, including ordinary full foot type, toe type (black/white), black foot type with deodorant, insole type with deodorant and other styles, and the use scene is more subdivided. The average heating temperature of the foot patch is about 40 °C, and it can continue to heat for 8-10 hours, the temperature is lower than that of the ordinary warm patch, the foot movement is more, and the skin is more sensitive, and the low temperature comfort is higher. Models with deodorant are effective in preventing foot odor caused by stuffiness and sweating. There are also pointed-toe styles designed for women's pointed-toe heels. The price of the foot sticker is about 6 yuan per pair, of which the full foot type is about 9 yuan per pair.
 
The warm paste of tung ash is mainly sold in Japan, and it needs to be purchased through overseas shopping or purchasing, and because of the heavy weight of iron powder inside, the price has almost doubled.