Bubble wrap, burlap and thick but not very heavy fabrics (could break branches/stems) can work. Remove the wrapping when the cold passes (remember that the plants may not be completely dormant so they need sunlight until the leaves brown out). Water the pot before the cold temperatures arrive. Check for insects in case the temps go down more than expected and you have to bring it indoors anyway. If you have a garage or shed, you can put the pot there as long as you remember to water it.

Austin has gotten into the teens before so remember that there are limits to how much protection these wrappings will give the plant.

Tropical hibiscus needs to be brought inside as it does not like temperatures below 50F.

Lynn, I am in east Texas. I always bring in my hibiscus, a hint of freeze will zap them. A garage, sunny window in the house will do fine if you dont have a greenhouse. Mine are in my greenhouse all winter with a little heater and do just fine. But I do not leave any out at all in freezing or near freezing temps. They will not make it.