Langkawi is an archipelago of 99 islands in the Andaman Sea, some 30 km off the mainland coast of northwestern Malaysia. The islands are a part of Malaysia’s Kedah state, but are adjacent to the Thai border. By far the largest of the islands is the eponymous Pulau Langkawi with a population of about 45,000. The island is a declared duty-free zone.
The peak season is from December to March when moonson at the eastcoast shuts down most of the Islands there (Perhentian etc.). This makes Langkawi a good island alternative during that time period. Generally though, Langkawi can be visited all year around.
Pulau Kapas is a small island located only about 6km off Marang in the east coast state of Terengganu (about 1h north of Kuala Terengganu). It has quite and relaxed atmosphere because it is bypassed by the majority of the backpacker circuit looking for a more remote place like the Perhentian Islands. Pulau Kapas only get fairly busy on the weekends when locals come to island. There are a few good snorkeling spots around the island. All accommodations and beach are on the west coast facing the mainland. The west coast is the weather side has no sand beach, only rocks - it can be reached after a short walk through the jungle. Pulau Kapas shuts down during the monsoon season between November and February.