Ireland's failure to prepare effectively for the humidity in Japan negatively affected their performance at the Rugby World Cup, Rory Best says.

The retired former Irish captain made his final international appearance in his side's heavy quarter-final defeat by New Zealand in October.

Best said Ireland underestimated the impact the humidity would have.

"People want definite answers as to what went wrong, but there just isn't one," he told 2fm's Game On.

He said the squad's pre-tournament training camp in Portugal was helpful, but that it did not do enough to fully prepare them for what they would face.

"We nailed the heat in Portugal but we possibly underestimated the effect the humidity would have, not on our conditioning but on our ability to handle the ball," he continued.

"I'm not big into gimmicks and when I heard about Wales were using baby oil on the ball, I thought it was just a nonsense - until I got out there and suddenly realised.

"I was drying my hands to throw the ball in but by the time you picked the ball up your hands were soaking because you were sweating so much.

"I think we could maybe have trained with dry balls to get confidence, but also trained with the ball soaking wet, to work out how our skill level could be improved by doing this.

"At the start we used an older ball which was more slippery but that tailed off a bit as the pressure of the games came on and you wanted to make sure you had enough confidence for them.

"I think, ultimately, we should have just been going right through thinking 'if these are the worst conditions we are performing in, then it is great because the games will be easy'."

Joe Schmidt's Ireland beat the All Blacks last year and were among the favourites to win the World Cup, but lost to the hosts in the group stages before being outclassed by the All Blacks in the last eight.

Best, who admitted considering reversing his retirement after receiving a number of club offers, also questioned whether an earlier arrival in Japan before the World Cup could have helped Ireland overcome the challenge of the humid conditions.

"It takes time to get used to the conditions and it was only as the tournament went on that our handling got better," he added.

"You're trying to balance being away from home for that extra length of time versus getting your preparations right. You have to find out what is right for your squad.

"Definitely, whatever we could have done to make the handling a bit more appropriate... maybe being out there earlier might have made a difference but you are dealing in hindsight."