Bubble cover - Bubbles up or down?

[Hot Tub Guru]

Does anyone know the best or proper way a bubble cover should sit on the water?  bubbles up or down? 

[Dr. Spa™ Ret.]

Doesn't matter. Flip it periodically to sanitize both sides.

[Hot Tub Guru]

Thanks.  But since the customer wanted it cut to fit flipping it might not work.  Any suggestions? 

[TwinCitiesHotSpring]

Thanks.  But since the customer wanted it cut to fit flipping it might not work.  Any suggestions?

bubbles down, I've never come across one on a pool or spa that was bubbles up

[Hot Tub Guru]

Since there is a 50/50 split on what is correct, I've decided to just replace the bubble cover for my customer.  This and all future installations will be bubbles down.

[Chas]

On an open pool or spa I always go bubbles down just because the smooth surface tends to hold less dirt than the bubbly side. But on a covered tub, I would defer to the good Doctor's advice.