This paper presents a cloth simulation system that can stably take large time steps, overcoming the limitations of previous methods that required small time steps to avoid numerical instability. The system uses an implicit integration method and a new technique for enforcing constraints on individual cloth particles. Cloth is modeled as a triangular mesh, with internal forces derived from a simple continuum formulation that supports modeling operations such as local anisotropic stretch or compression. A unified treatment of damping forces is also included. The implicit integration method generates a large, sparse linear system at each time step, which is solved using a modified conjugate gradient method that simultaneously enforces particles' constraints. The constraints are maintained exactly, independent of the number of conjugate gradient iterations. The resulting simulation system is significantly faster than previous cloth simulation systems. The paper discusses the challenges of cloth simulation, including the stiffness of the underlying differential equation and the computational cost of explicit methods. It introduces a simulation system that uses a triangular mesh for cloth surfaces, eliminating topological restrictions of rectangular meshes, and a simple but versatile formulation of the internal cloth energy forces. A key step in the simulation process is the solution of an O(n) × O(n) sparse linear system, which arises from the implicit integration method. The system also introduces a simple, unified treatment of damping forces and dynamically adapts time steps during the simulation. The paper compares the proposed method with previous work, highlighting the advantages of the implicit integration method and the direct constraint satisfaction approach. It describes the simulation architecture, energy and forces, sparse matrices, constraints, and implicit integration. The system is shown to be efficient and effective, with results demonstrating realistic cloth behavior and performance on a variety of simulations. The paper concludes that the implicit integration method and direct constraint satisfaction are powerful approaches that allow for large time steps and efficient simulation of cloth.This paper presents a cloth simulation system that can stably take large time steps, overcoming the limitations of previous methods that required small time steps to avoid numerical instability. The system uses an implicit integration method and a new technique for enforcing constraints on individual cloth particles. Cloth is modeled as a triangular mesh, with internal forces derived from a simple continuum formulation that supports modeling operations such as local anisotropic stretch or compression. A unified treatment of damping forces is also included. The implicit integration method generates a large, sparse linear system at each time step, which is solved using a modified conjugate gradient method that simultaneously enforces particles' constraints. The constraints are maintained exactly, independent of the number of conjugate gradient iterations. The resulting simulation system is significantly faster than previous cloth simulation systems. The paper discusses the challenges of cloth simulation, including the stiffness of the underlying differential equation and the computational cost of explicit methods. It introduces a simulation system that uses a triangular mesh for cloth surfaces, eliminating topological restrictions of rectangular meshes, and a simple but versatile formulation of the internal cloth energy forces. A key step in the simulation process is the solution of an O(n) × O(n) sparse linear system, which arises from the implicit integration method. The system also introduces a simple, unified treatment of damping forces and dynamically adapts time steps during the simulation. The paper compares the proposed method with previous work, highlighting the advantages of the implicit integration method and the direct constraint satisfaction approach. It describes the simulation architecture, energy and forces, sparse matrices, constraints, and implicit integration. The system is shown to be efficient and effective, with results demonstrating realistic cloth behavior and performance on a variety of simulations. The paper concludes that the implicit integration method and direct constraint satisfaction are powerful approaches that allow for large time steps and efficient simulation of cloth.