Corrections Minister Kelvin Davis is backing a decision to spend more than a million dollars on slushy machines for prison staff.

Corrections bought 193 slushy machines to cool down staff during the hot summer months.

Opposition leader Simon Bridges has slammed the spending as irresponsible and wasteful.

But Davis says Corrections was right to consider the health and well-being of officers wearing gear that weighs up to six kilos.

"It gets up to 30 degrees. They're working in a very dangerous, tense environment, and I think that anything we can do to help alleviate the heat and that - good on Corrections, they are looking after the workers."

Davis says that he has been informed by Corrections that research has found that ice machines are the quickest way for reducing core body temperatures. 

He says that prison guards are hard working and have a tough job to do, which their heavy uniform doesn't make any easier. 

"I challenge anybody to throw on six kilograms worth of gear and walk around in 30 degree heat for eight hours a day." 

Police are also affected, Davis says, as they have to wear a similar weight, but have the benefit of air-conditioned cars that prison guards don't have. 

He says that anyone who picks apart this policy is not focused on the bigger picture. He rejects Simon Bridges complaints, saying that there is no "car too small" for him to bark at. 

• $1 million spent on slushy machines for prison guards

Davis says that any questions around the validity of the research and whether the slushy machines were value for money need to be directed to Corrections.