Polyurethane adhesives are generally known as ‘reactive adhesives’. This means they undergo chemical reactions to transition from a liquid or semi-liquid state to a solid state (1). In this case, the reaction is with moisture, either in the air or from the substrates being bonded. These adhesives react with the moisture to form strong chemical bonds, creating a tough adhesive layer. Our Subfloor Adhesive, for example, will dispense from the can as a gel then expand and harden.
This image shows one of our adhesives curing on the left, and on the right you can see the fully cured bubbles:

The drying time of polyurethane adhesives is primarily governed by the rate of this reaction. A common misconception is that higher ambient temperatures will accelerate this process. Earlier this month I met a home builder at the Texas Sunbelt Builders Show in Fort Worth that thought this. In reality, it’s the humidity that plays a more substantial role (2). Increased humidity will provide more moisture for the reaction, accelerating the curing process. We get frequent reports from customers in humid climates that align with this.
In the below Will It Foam Bond 60 video (the section I’m referring to starts at 1:49), our product manager describes how the humidity impacts the curing process. In the case of this video, it was a low humidity day, resulting in a longer curing process:

According to a study published in the International Journal of Adhesion and Adhesives, a typical one-component polyurethane adhesive can take between 24 to 48 hours to fully cure at room temperature and average humidity conditions (3). This duration can reduce to several hours in high humidity environments or extend beyond two days in extremely arid conditions.
TYTAN Professional Adhesives are all within the 24-48 hour window described above. With Subfloor Adhesive and Drywall Adhesive being 48 hours to fully cure, and Foam Bond 60 fully curing in 24 hours. Even more impactful for our customers, however, is the skin time. The skin time for Subfloor Adhesive and Drywall Adhesive is 20 minutes. The skin time for Foam Bond 60 is even faster at 2-5 minutes. The below section describes the difference.