SIGA Majrex: A Skin Like the Cactus

What can we learn from the cactus related to building science? The cactus “skin” has essentially two perm ratings. The cactus absorbs vapor through its skin at night, and in the daytime when temperatures rise, that same skin prevents the moisture from escaping. The skin of the cactus allows moisture to migrate inward, but not outward.
SIGA has learned the answer to keeping walls dry by incorporating the unique characteristic of the skin of the cactus to collect and store water. In our buildings, we want the opposite to happen — prevent moisture from getting into our walls and allow it to migrate out. SIGA’s new product Majrex does just that.

While a cactus needs water to survive, our walls do not. In fact, moisture in our walls has the opposite impact — effectively “killing” our walls instead of nurturing them. So, the goal is the reverse of the cactus.
Humidity/moisture is higher inside our buildings due to such activities as cooking, showering and many other sources, even breathing. That moisture gets into our walls through a couple mechanisms, including air infiltration. With air infiltration, air and the moisture it carries travels from the interior of the building into the walls. That moisture within the air then condenses on cold surfaces in the interior of the walls — like a “sweaty” glass of ice water on a humid summer day. While it is best to keep the air out of our walls in the first place, some air will get in regardless carrying moisture with it.

At the point we have condensation in our walls, we absolutely need that moisture to dry or migrate out of the walls. Moisture in our walls causes mold, mildew and dry rot. In a typical home, if we were to add up all the cracks in the walls, corners and around the windows and doors, we have a hole equal to a 3-foot by 3-foot window open 24 hours every day of the year. Not only does this make us cold, but it also empties our pockets. Most importantly, it enables moisture to get into our walls with air as its transport mechanism.

SIGA patented its unique, one directional moisture transport and named it Hygrobrid technology. With this technology, SIGA developed Majrex, a “smart” interior membrane. Majrex has two different perm ratings. The perm rating from interior of the building to the interior of the walls is less than 0.097. In the other direction, from the interior of the wall to the interior of the building, the perm rating is greater than or equal to 4.25. Unlike other “smart” membranes that react to humidity and become more permeable to moisture, Majrex is essentially vapor open one way and nearly vapor closed the other. Combined with the SIGA Majvest air and weather barrier on the exterior with its 68-perm rating, we can effectively keep air and moisture out of our walls and effectively enable our walls to dry to the interior or to the exterior.


Majrex offers the benefits of:
1. Making our walls airtight so air and moisture cannot get in.
2. Making sure walls are vapor open, enabling moisture to migrate out of the walls.

Unfortunately, we often hear from building practitioners that walls need to breathe, and there is a very important distinction we would like to make. We do not want air going into our walls, because that very air is the culprit which brings moisture into our walls. We do not want them to “breathe.” Instead, we want them to be vapor open.

Simply put, Majrex is a directional membrane which allows moisture out of our walls and prevents it from coming in. Thanks to the cactus, SIGA has learned the secret to keeping our walls dry.

For more information or to order SIGA Majrex, call us at 720.287.4290