The insulating core inside the hot tub cover is surrounded by plastic to keep water from soaking the foam, but it is normal for small amounts of water or condensation to find their way in between the plastic and the outer vinyl layer. Your spa cover should have small holes on the underside to allow this water to drain out.
If your cover has taken in a large amount of water, you probably have cause for concern. Check for any punctures or tears in each of the layers, especially around the perimeter seal. In some cases, this is something you can repair yourself.
Once you have located any tears or holes, you’ll need to drain as much of the water out of the liner as possible. Stand the core up, with the hole the water entered through at the bottom, and let the water drain out. If you are unable to get the majority of water out through the original tear, then it is likely that water has seeped in and reached the foam core. At this point, it will be necessary to purchase a replacement hot tub cover.
Fortunately, with Core Covers, the outer vinyl is treated to resist mildew, and our scientifically formulated plastic layer is much more water resistant than typical plastic covers. In fact, Core’s Vapor Lock Seal has proven to be four times more effective than other seals at protecting the foam core from water absorption.