I don't think there's any harm in thicker, and it's not too expensive. Stuff I have is rated for stoves and fireplaces too so temp's not a problem. I presume the tape's a little more flexible so you may want a mixture. I don't know if painting over the tape is ideal....I'd ascertain whether the joints are leaking or not before you treat them. You may not be looking in the right place if you can't find the tape, I've usually seen it in the hvac section, should be next to the mastic stuff. Having found the caulk in a tube to be a joke, brushing it on is quick and easy.

I like the mastic tape and use Hardcast brand, but surfaces have to be clean and dry for the tape to adhere. I've also used the material countrybomo posted..but when I used it the first mastic application would fill most of the woven areas once it dried the second application of mastic would make complete seal. So for me..the mastic tape works best..with clean surfaces. while you are shopping your hvac supply store ask for foil faced duct wrap..R-8 and the tape of similar material to seal the seams. The wrap will install after you have completed the sealing work.The larger gaps that you have mastic sealed will now be well insulated with R-8. The wrap has a foil faced paper with a nylon scrim and fg insulation backing. You'll want a sharp blade to cut it. cut your duct wrap in to sections. tape one end of wrap to surface wrap remainder around & under trunkline. You want the fg insulation in full contact with the metal trunk line. But not pulled so tightly as to compress the insulation and reduce R-value. A stapler for duct wrap will help to hold the sections and give them support while you cut & peel the backing off the tape. I don't have much faith in the foil bubble foil products, as install is hardly ever done properly with spacers and the performance is over rated. best of luck.

David, I live in dry CA and honestly have not done any research on how it affects humid environments so my experience can't offer you much help. Did it work? It helped reduce my electric usage immediately and the air temp differential from a vent dropped by about 3 degrees immediately. I didn't test much after that, but the before/after differential was done two days apart at the same time of day. I was keeping my thermostat between 81 and 83 (damn sweaty hot) and still had a $400/mo pge bill (~1700kwh) and after the RB I kept it at 77 and the bills were between 10 and 20% lower. The bills compared year-to-year were so much lower over 12mo period (20%?) that the utility gave me some kind of automatic refund. I bought my stuff from Horizon (savenrg.com). They are in Phoenix AZ where the climate is a bit worse than mine, but similar. They aren't a flashy company, obvious from their site, but their material made so much sense when I confirmed from other sources. It's not cheap. The owner also helped teach me the DIY w/duct sealing: making sure all joints are tight (ties/metal straps), lathering on tons of mastic on them, and applying metal backed tape where needed. Dust is the #1 killer of a radiant barrier. Their site explains it and how multiple layers of reflectivity, when separated adequately (scrim), keep the RB working even when dusty on the top layer. The RB on the floor, above the insulation, is triple layer. The ducts are wrapped with their ducting RB which is double layer and I put the triple layer on the top-parts where the dust might collect. Either way, I'm not taking chances as I'm having my roof replaced and afterward I'm going to cleanup & dust where it's easy to do so. After the 15 months I went back up to check out dust and it was very minimal, except directly under the dormer vents where a handful of smaller leaves/dirt had dropped. Ducting: That's existing flex ducting (r4/5 don't recall) wrapped w/multi-layer RB. RB under Roof I'm not sure it will help all that much to put RB under the roof when it's already on the attic floor + ducting like mine. Their site also talks about this. IMO I'd be creating an oven situation, but in reality I don't know if it matters. I currently have shake roof w/stick frame so it slightly breathes there and through the ventilation at night. However, once it goes to OSB w/composite shingles, I'm relying on the vents anyway. The roofing salesmen say "sure it helps, anytime you can prevent heat from entering the attic in the first place is good" as they try to sell the OSB w/tiny bit of foil on the bottom of it. I don't know if that works w/out creating conductive heat transfer that then radiates in the attic. As far as whacky CA rules, yeah no kidding. I honestly think in certain parts of CA they should've left the R alone and just suggested RB properly installed. I was hoping bluelogic would've been subscribed to his original thread and could tell us what happened with his project.

Energy, the installing contractor has already demonstrated that they don't think it is their problem. I should have written my response differently. I think that the OP needs an inspector that is competent with moisture/mold issues. I think that they need an independent authority to confront the contractor, if is is an HVAC problem and to guide them to fixing other problems if it is not HVAC. I agree that It would be better if this person is not someone that does remediation and stands to profit further. The single picture that was posted, and the description indicate that there could be severe damage much like a home with a burst water heater or other standing water in the house for weeks. At the very least, there is a lot of clean-up that needs to be done and a lot of that is beyond the capability of an average home owner. I find it difficult to believe that, even with heavy rain, a properly-designed HVAC in a normal house would do that. The evidence points the new HVAC system as the culprit assuming that is only thing that changed in this house, and that mold has never been a problem. Now they have an unlivable home with "...mold on everything.... " The OP needs data (humidity) and an independent source of advice to confront the contractor and maybe for court. This is going to be an expensive mess to fix, with either sweat equity or for contractors. OP, start with general home inspectors like the one that did your home inspection when you purchased the house. Look for one that has personnel that has specialized training in mold and moisture issues within that group. Your best bet might be to look at larger firms first that have several inspectors. With some luck, you might find someone that can tap expertise in s a certified Home Efficiency Ratings System(HERS), Residential Energy Services Network (RESNET) Member and experience in the mold remediation industry all under one roof. It is likely to cost some hundreds, but with your problem, I think it will be money well spent. Put in a call to your insurance agent as well.