The double bottle warmer for twins can heat two bottles at one time. So it's a perfect choice for parents with twins or other multiples. While the single bottle warmer only can heat up one baby bottles. The design of single bottle warmer is more compact than the double one, so it will not take up more counter spaces in the kitchen or bedside. Besides, it takes less time to heat up the milk with a single bottle warmer than with a double bottle warmer. And the opening cover of double bottle warmer is suitable for all sizes of baby bottles and material milk bottles, while the single bottle warmer should put the standard milk bottles in it.