Anything without a heat source won't really do the trick in the trunk of your car. Whether its an insulated cooler or a blanket. From an engineering major here, All insulation does is slow down heat transfer. So if your balls started warm, and you wrapped them in a blanket, it may keep them warm longer but eventually they will get just as cold as their surroundings. The reason you stay warm under a blanket is that your body produces heat and the blanket keeps that heat from leaving easily. But your bowling balls dont produce heat, and regardless of the amount of insulation they will eventually get cold. One idea I do have for a heat source, is with that styrofoam cooler (or any regular plastic cooler for that matter - if you can afford one). There is a product called hothands, which is a personal hand warmer. I use them all the time hunting, and they provide heat for about 4 hours. It never gets too hot, cuz you can hold them in your bare hands. Take one of these every night and tape the edges to the inside of the cooler lid. They need air to work, so dont seal them up against the lid. Keeping it on the lid should provide heat to the cooler, but be far enough away from your balls to keep them from getting unevenly heated and further risking cracking.

Sorry for my wall of text, but hope I was able to help.

I know we're all just tempting fate with these replies, but...

I leave all my current stuff in the trunk.  It's been about 25* every morning this week.  It's 34* now, and the bowling center will be somewhere between 70-75* when I go to leagues.  It will probably take a full game before the balls warm up and aren't freezing to the touch.

I'm not overly thrilled about the concept of throwing frozen balls down the lane - mainly because they don't seem to react very well until they are warmed up, but also from the stress and abuse of throwing them down the lane - but, I've never had a problem.

I keep the rest of my stuff in the detached, unheated and uncooled garage.  Summer time the temps get up to 95 in there, and last winter I believe they got as low as 13.

I have this thermometer out there with the sensor hanging just above head level (probably 7 ft) and it stores the max and min temperatures.

The only balls that I've had crack on me were sitting in the house which is kept at 70* all year.  All but one had some sort of plug work, and the one that didn't was a blem.

If you're that worried about it, a cooler might help.  They are just designed to help maintain the temperature, so cold will stay cold and warm will stay warm.  It won't do it forever, and I guess maybe eventually it will reach some sort of equalibrium.   I know that I've had coolers full of ice in the summer and several days later you still have ice in the water.

Not a good idea. It doesn't really matter if the ball didn't crack or whatever.....you were fortunate that's all. In regards to storage ......where there's a will there's a way...........

Until recently, for the last 20 years, I lived on a 3rd floor condo (no elevator) and the parking spot could be as much as 3 blocks away. And I have more than few balls, so I took a 3 pronged approach:

1) Rented a locker at the two houses I bowl at most
2) carried 1 or 2 balls with me in the car-----but,
3) was careful not to leave my best/newest equipment in the car

Also...  although I didnt relish lugging the balls over 3 blocks in a 2 ball tote (no wheels) and up the 3 flights of stairs, when the temps outside were lower than 20 or higher than 80, I did just that.

Still...  I have occasionally forgotten to bring them in and tehy have sat the whole night in below zero weather, and have never had a ball crack.

So....  as a practice, I wouldnt recommend leaving them outside in extreme weather (anything not between 20 and 80 degrees), but I also agree that as long as you give the ball at least 10-15 minutes to adjust to the inside temperature before throwing (or dropping!) it, that the odds are it will usually not be a problem.

However, my opinion is based only on my personal experience over 40 some years of bowling. It is not based on any special tecnical knowledge.

If you keep them in a bag you should be alright. I live in Montana and I have occasionally left my equipment outside over night in a trunk of a car. Only 1 time has it bit me in the ass, had 3 balls in the trunk, 2 inside of a bag, one not, the one that was left outside of the bag ended up cracking (cell). The other 2 balls were just fine. I thought the cell was going to be fine too, didn't crack till 2-3 days later sitting in my living room.

How about an ice chest......with or without a hot water bottle of some kind?

I don't go to college but what I do is carry my equipment in with me when I go to work.  Some jack azzes heckle me but I don't care I'd rather not take a chance.  The slow change in temperature doesn't affect the equipment like everyone else says...but I have had a Too Hot crack from sitting in the trunk for a few days during the winter.

I don't know if you'd consider bringing your equipment in class but it's an idea.
--------------------
The original Pin Krusher