What is the difference between Flex Gel and Flex Saline?

When choosing between gel and saline EEG sensors, it’s important to understand the advantages and trade-offs of each option. Both offer unique benefits depending on the context of your experiment or clinical use.

Ease of setup

Saline sensors are significantly faster and easier to set up than gel sensors, making them ideal for shorter sessions or environments where convenience is a priority. When properly moistened, saline sensors deliver signal quality that is comparable to gel. However, the noise floor may be slightly higher, especially if the contact quality is suboptimal.

Signal quality and preparation

Gel sensors can offer exceptionally low contact impedance, particularly when the skin is properly prepared. This often involves gently abrading the surface of the scalp to remove the superficial layer of the stratum corneum (the dry outer layer of skin) before applying the gel. While this process enhances signal quality, it also adds time to setup and may not be well-tolerated by children or individuals sensitive to discomfort.

Duration of use

For extended recordings, gel sensors are generally more reliable. They can maintain stable contact and quality signals for many hours without requiring adjustment. In contrast, saline sensors are more susceptible to signal degradation over time due to evaporation—typically after about an hour. This effect is more pronounced in hot, dry environments or at high altitudes.

Extending saline sensor usability

If longer sessions with saline sensors are necessary, there are ways to prolong their effectiveness:

• Add a non-volatile component such as glycerin to the saline solution to reduce evaporation.
• Top up the fluid periodically—for example, every 30 minutes—by applying more saline through the rear of each sensor.

Summary

• Gel sensors are ideal for extended, high-quality recordings but require more preparation time.
• Saline sensors are more user-friendly and efficient for shorter sessions, with comparable performance when adequately moistened.