It seems to me that this is a wives tale that may have some merit, but probably serves to sell more bat warmers to protect increasingly more expensive bats. Advanced composites have been around of years/decades in the aviation industry and those aircraft are not grounded when its cold. The manufacturers warn about using composites below 60F, not because of the bat construction, but rather because the ball becomes harder in colder weather.
That being said, I'd like to know more on the subject, but there seems to be little definitive information available other than broad generalizations about use below 60F.....
Bat warmers are legal only in USSSA and NSA that I am aware of. ASA and FED specifically ban bat warmers, or any other method of artificially warming the bat.
Comp, this would be an NSA tournament. NSA & USSSA are dominant in our area and we rarely ever have to worry about the temperature but this weekend has forecasts in the 40's & 50's.
DD occasionally uses her composite in the cages and cold weather and her bat has not had an Issue. She does not make a habit of it though. I would just use the composite bat and take your chances.
Up here in New England 95% of my daughters high school season is played in temps less than 60 and they have never had a problem with any of thier composite bats
I've seen a cf4 literally explode like a grenade on a well hit ball it the early spring (around 45-50°) pieces of shrapnel went flying everywhere! Maybe it was an isolated indecent and would have happened on an 80° day, but it scared me enough to have my dd only swing her Anderson bats in weather below 55-60°…