The temp that 100% cotton shrinks is at 60 degrees although 100% cotton shrinks more at 90 degrees.
To prevent cotton from shrinking in the dryer you should use the low heat setting or air fluff setting or delicate setting on the dryer and wash the cotton in water temperature lower than 60 degrees.
Air fluff does not shrink clothes as air fluff spins the clothes without any use of heat.
And the delicate setting uses a small amount of warm air to help dry the clothing but air fluff uses no heat so the clothes won't shrink.
Both delicate and air fluff settings eliminate shrinkage of clothing.
Air fluff on a dryer means that the dryer drum rotates and ambient air is circulated through the dryer drum without turning the heating element on.
No heating element is turned on when using the air fluff setting on your dryer and instead room temperature or normal air temperature is used to dry your laundry.
This means that cold air will gently move through the fabric and allow them to relax and release wrinkles without applying any heat.
The air fluff cycle on your dryer can be very efficient on delicate clothes.
The air fluff dryer cycle uses no heat (as you can guess with its name) and no intense spinning.
With light air and smooth shifting, clothes float around until they become dry.
Air drying or air fluffing helps to remove dust and fluff up your garments when they've lost their volume from hanging in the closet or lying folded in a drawer.
Since the dryer doesn't produce any heat for this setting, you should use it for items that are already dry.
The two settings on a dryer that eliminate shrinkage are delicate and air fluff.
The delicate setting on the dryer uses a very small amount of warm air to help dry your clothing, and air fluff spins clothes without any use of heat.
Delicates: Low heat, so drying time will be longer.
It is best to use this setting to use for delicate fabrics.
Permanent Press: Medium heat while drying and is best used for colored fabrics.
Air Fluff: Not used for drying.
Avoiding heavy duty cycles, fast spins and high-heat drying can also prevent shrinkage.
Use delicate cycles instead, and place delicate clothes in a mesh laundry bag for added protection.
When drying, consider a low-heat or air dry setting.
When in doubt, always follow the instructions on your garment's care tag.