Will these fit a standard split king?

No. The fitted sheet is split only across the top half, so it suits split-top or FlexTop mattresses. A standard split king has two separate twin XL halves and needs two fitted sheets.

Do they work on an adjustable base?

Yes, that is the point. Each side of the head half moves independently, and the corner straps plus full elastic help keep the fitted sheet in place as the bed articulates.

What comes in the set?

One flat sheet, one split-top fitted sheet and two king pillowcases. There is no second fitted sheet, unlike split king sets sold as two halves.

What are the dimensions?

The flat sheet is 110 by 104 inches, the fitted sheet is 78 by 80 inches, and the pillowcases are 20 by 40 inches.

Is the fabric good for hot sleepers?

The fabric is described as breathable and hypoallergenic. It is a performance-style weave rather than crisp cotton percale, so expect a soft hand rather than a cool, linen-like feel.

How should I care for them?

They are made to be easy to care for. Wash with like colors and follow the care label; the reinforced elastic and straps are the parts most likely to wear first.