As if the holiday season wasn’t enough of a productivity problem, it turns out that Christmas decorations can cause network problems.

Wireless networks are often unreliable—they’re succeptible to interference and problems with unwanted reflections. A survey by wireless networking company AirMagnet shows that typical office decorations can reduce signal strength by 25%.

“When new elements are introduced… they have the potential to seriously affect the performance of the Wi-Fi network, by deflecting, absorbing or otherwise interfering with the wireless signal,” says Chia-Chee Kuan, CTO and vice president of engineering for AirMagnet. “During the holidays, it could be the decorations in an office, at other times it could just as easily be a new microwave oven or a metal shelving unit.”

If you need a solid, reliable network in your office, then proper Ethernet cabling will always be more effective than wireless networks—no matter what the advertising brochures claim.