ThisIsCarpentry.com says this about wood expansion:
Wood is hygroscopic, which means its MC (moisture content) will fluctuate based on the relative humidity (RH)of the surrounding air. As humidity increases, the MC increases, and the wood expands, and as the humidity decreases, MC decreases, and the wood shrinks. This relationship is referred to as Equilibrium Moisture Content (EMC), and can be accurately predicted.
Most clarinets are made of Grenadilla, or African Blackwood, which, you guessed it, behaves exactly the way every other wood does.
So, here's the scoop, and this is the simple explanation. Your clarinet gets cold; the tube shrinks. As it warms, the tube expands. If the inside of the tube expands (by means of you blowing AIR into it) before the outside has a chance to warm up, your wooden clarinet is likely to crack.
For some more intelligent talk on the topic of clarinet cracks and repairs, you can check out some of these links:
Anatomy of a Clarinet Crack Repair
Avoiding Cracking In Wooden Clarinets
Finally, we'll call it a day by listening to the original Canon by Pachelbel (not Taco Bell, guys, let's get that PERFECTLY understood), and then by watching the next guy gripe about it.
Blogging about reeds? I must be MAD!
.Here are some tools and tips of the clarinet and reed trade for younger players to supplement the musical education received from band directors and music teachers. I've tailored these methods (used by professional clarinet players!) to be accessible and user-friendly for the beginner to intermediate clarinet reed-hater.